Assignments Class 12 Chemistry The p – Block Elements

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The p – Block Elements Assignments Class 12 Chemistry

Question. Which of the following statements are correct?
(A) S–S bond is present in H₂S₂O₆.
(B) In peroxosulphuric acid (H₂SO₅) sulphur is in +6 oxidation state.
(C) Iron powder along with Al₂O₃ and K₂O is used as a catalyst in the preparation of NH₃ by Haber’s process.
(D) Change in enthalpy is positive for the preparation of SO₃ by catalytic oxidation of SO₂.

Question. Bond dissociation enthalpy of E-H (E = element) bond is given below. Which of the compounds will act as strongest reducing agent?

(A) NH₃
(B) PH3
(C) AsH₃
(D) SbH₃

Question. On heating with concentrated NaOH solution in an inert atmosphere of CO, white phosphorus gives a gas. Which of the following statement is incorrect about the gas?
(A) It is highly poisonous and has smell like rotten fish.
(B) It’s solution in water decomposes in the presence of light.
(C) It is more basic than NH₃.
(D) It is less basic than NH₃.

Question. A brown ring is formed in the ring test for NO₃^– ion. It is due to the formation of:
(A) [Fe(H₂O)₅(NO)]²⁺
(B) FeSO₄.NO₂.
(C) [Fe(H₂O)₄(NO)₂]²⁺
(D) FeSO₄.HNO₃.

Question. Which of the following statements are true?
(A) Only types of interactions between particles of noble gases are due to weak dispersion forces.
(B) Ionisation enthalpy of molecular oxygen is very close to that of xenon.
(C) Hydrolysis of XeF₆ is a redox reaction.
(D) Xenon fluorides are not reactive.

Question. Hot conc. H₂SO₄ acts as moderately strong oxidising agent. It oxidises both metals and non-metals.Which of the following element is oxidised by conc.
H₂SO₄ into two gaseous products?
(A) Cu
(B) S
(C) C
(D) Zn

Question. Which of the following elements can be involved in pp–dp bonding?
(A) Carbon
(B) Nitrogen
(C) Phosphorus
(D) Boron

Question. Which of the following are peroxoacids of sulphur?
(A) H₂SO₅ and H₂S₂O₈
(B) H₂SO₅ and H₂S₂O₇
(C) H₂S₂O₇ and H₂S₂O₈
(D) H₂S₂O₆ and H₂S₂O₇ 

Question. Which of the following orders are correct as per the properties mentioned against each?

Question. Which of the following statements is wrong?
(A) Single N–N bond is stronger than the single P–P bond.
(B) PH₃ can act as a ligand in the formation of coordination compound with transition elements.
(C) NO₂ is paramagnetic in nature.
(D) Covalency of nitrogen in N₂O₅ is four. 

Question. In the preparation of compounds of Xe, Bartlett had taken O₂⁺PtF₆^– as a base compound. This is because
(A) both O₂ and Xe have same size.
(B) both O₂ and Xe have same electron gain enthalpy.
(C) both O₂ and Xe have same ionisation enthalpy.
(D) both Xe and O₂ are gases.

Question. Which of the following does not react with oxygen directly?
(A) Zn
(B) Ti
(C) Pt
(D) Fe

Question. Affinity for hydrogen decreases in the group from fluorine to iodine. Which of the halogen acids should have highest bond dissociation enthalpy?
(A) H-F
(B) HCl
(C) HBr
(D) HI U

Question. Reduction potentials of some ions are given below.Arrange them in decreasing order of oxidising power.

(A) ClO₄^– > IO₄^– > BrO₄^–
(B) IO₄^– > BrO₄^– > ClO₄^–
(C) BrO₄^–> IO₄– > ClO₄^–
(D) BrO₄^– > ClO₄– > IO₄^–

Question. Main source of helium is
(A) Air
(B) Radium
(C) Monazite
(D) Water

Question. Which of the following statements are correct for SO₂ gas?
(A) It acts as bleaching agent in moist conditions.
(B) Its molecule has linear geometry.
(C) It can be prepared by the reaction of dilute H₂SO₄ with metal sulphide.
(D) All of the above

Question. Which of the following is iso-electronic pair?
(A) ICl₂, ClO₂
(B) BrO₂^–, BrF₂ ⁺
(C) ClO₂, BrF
(D) CN^–, O₃ A

Question. Which of the following reactions is an example of redox reaction?
(A) XeF₄ + O2F₂ → XeF₆ + O₂
(B) XeF₂ + PF₅ → [XeF]+[PF₆]^–
(C) XeF₆ + H₂O → XeOF₄ + 2HF
(D) XeF₆ + 2H₂O → XeO₂F₂ + 2HF

Question. A black compound of manganese reacts with a halogen acid to give greenish yellow gas. When excess of this gas reacts with NH3 an unstable tri-halide is formed. In this process the oxidation state of nitrogen changes from:
(A) – 3 to +3.
(B) – 3 to 0.
(C) – 3 to +5.
(D) 0 to – 3.

Question. Which one of the following does not exist?
(A) XeOF₄
(B) NeF₂
(C) XeF₂
(D) XeF₆ 

Question. In which of the following reactions conc. H₂SO₄ is used as an oxidising reagent?
(A) CaF₂ + H₂SO₄ → CaSO₄ + 2HF
(B) 2HI + H₂SO₄ → I₂ +SO₂ + 2H₂O
(C) Cu + 2H₂SO₄ → CuSO₄ + SO₂+ 2H₂O
(D) NaCl + H₂SO₄ → NaHSO₄ + HCl

Question. Which of the following statements are true?
(A) Only types of interactions between particles of noble gases are due to weak dispersion forces.
(B) Hydrolysis of XeF6 is a redox reaction.
(C) Xenon fluorides are not reactive.
(D) None of the above.

Question. When XeF₄ is partially hydrolysed, it yields
(A) XeSO₃
(B) XeOF₂
(C) XeOF₄
(D) XeF₂

Question. Complete the following reaction: Xe + PtF₆ →
(A) Xe + PtF₆ → XeF₄ + PtF₂
(B) Xe + PtF₆ → XeF₆ + Pt
(C) Xe + PtF₆ → Xe+[PtF₆]^–
(D) Xe + PtF₆ → XeO₂F₄ + Pt

Question. Which of the following is not tetrahedral in shape?
(A) NH₄ ⁺
(B) SiCl₄
(C) SF₄
(D) SO₄²⁻

Question. The shape of XeF₄ is
(A) tetrahedral
(B) square planar
(C) pyramidal
(D) linear

Question. Which of the following statements are correct?
(A) Among halogens, radius ratio between iodine and fluorine is maximum.
(B) Leaving F – F bond, all halogens have weaker X – X bond than X – X’ bond in inter-halogens.
(C) Among inter-halogen compounds maximum number of atoms ate present in iodine fluoride.
(D) Inter-halogen compounds are more reactive than halogen compounds.

Question. On heating ammonium dichromate and barium azide separately we get
(A) N₂ in both cases
(B) N₂ with ammonium dichromate and NO with barium azide
(C) N₂O with ammonium dichromate and N₂ with barium azide
(D) N₂O with ammonium dichromate and NO₂ with barium azide

Question. Which one of the following elements is most metallic ?
(A) P
(B) As
(C) Sb
(D) Bi

Question. The correct decreasing order of basic strength is:
(A) AsH₃ > SbH₃ > PH₃ > NH₃
(B) SbH₃ > AsH₃ > PH₃ > NH₃
(C) NH₃ > PH₃ > AsH₃ > SbH₃
(D) PH₃ > AsH₃ > SbH₃ > NH₃

Question. Maximum covalency of nitrogen is __________.
(A) 3
(B) 5
(C) 4
(D) 6

Question. The three important oxidation states of phosphorus are
(A) –3, +3 and +5
(B) –3, +3 and –5
(C) –3, +3 and +2
(D) –3, +3 and +4

Question. A deep brown gas is formed by mixing two colourless gases which are
(A) NO₂ and O₂
(B) N₂O and NO
(C) NO and O₂
(D) NH₃ and HCl

Question. Nitrogen is relatively inactive element because
(A) its atom has a stable electronic configuration
(B) it has low atomic radius
(C) its electronegativity is fairly high
(D) dissociation energy of its molecule is fairly high

Question. Liquid ammonia bottles are opened after cooling them in ice for sometime. It is because liquid NH₃
(A) Brings tears to the eyes
(B) Has a high vapour pressure
(C) Is a corrosive liquid
(D) Is a mild explosive

Question. Pick out the wrong statement.
(A) Nitrogen has the ability to form pπ-pπ bonds with itself.
(B) Bismuth forms metallic bonds in elemental state.
(C) Catenation tendency is higher in nitrogen when compared with other elements of the same group.
(D) Nitrogen has higher first ionisation enthalpy when compared with other elements of the same group.

Question. Pure nitrogen is prepared in the laboratory by heating a mixture of
(A) NH₄OH + NaCl
(B) NH₄NO₃ + NaCl
(C) NH₄Cl + NaOH
(D) NH₄Cl + NaNO₂.

Question. Among the 15th group elements, as we move from nitrogen to bismuth, the pentavalency becomes less pronounced and trivalency becomes more pronounced due to
(A) Non metallic character
(B) Inert pair effect
(C) High electronegativity
(D) Large ionization energy

Question. NH₃ gas is dried over :
(A) CaO
(B) HNO₃
(C) P₂O₅
(D) CuSO₄

Question. Pentavalence in phosphorus is more stable when compared to that of nitrogen even though they belong to same group.
This is due to
(A) dissimilar electronic configuration
(B) due to presence of vacant d-orbitals
(C) reactivity of phosphorus
(D) inert nature of nitrogen

Question. Which one of the following is not an use of ammonia ?
(A) To produce various nitrogenous fertilizers.
(B) In manufacture of nitric acid
(C) As a refrigerate
(D) In the pickling of stainless steel

Question. Most acidic oxide among the following is –
(A) N₂O₅
(B) P₂O₅
(C) N₂O₄
(D) As₂O₃

Question. Which of the following species has the highest dipole moment?
(A) NH₃
(B) PH₃
(C) AsH₃
(D) SbH₃

Question. Which oxide of nitrogen is obtained on heating ammonium nitrate at 250ºC ?
(A) Nitric oxide
(B) Nitrous oxide
(C) Nitrogen dioxide
(D) Dinitrogen tetraoxide

Question. Which of the following fluorides does not exist?
(A) NF₅
(B) PF₅
(C) AsF₅
(D) SbF₅

Question. Ionic radii (in Å) of As³⁺, Sb³⁺ and Bi³⁺ follow the order
(A) As³⁺ > Sb³⁺ > Bi³⁺
(B) Sb³⁺ > Bi³⁺ >As³⁺
(C) Bi³⁺ > As³⁺ > Sb³⁺
(D) Bi³⁺ > Sb³⁺ > As³⁺

Question. With respect to protonic acids, which of the following statements is correct ?
(A) PH₃ is more basic than NH₃
(B) PH₃ is less basic than NH₃
(C) PH₃ is equally basic as NH₃
(D) PH₃ is amphoteric while NH₃ is basic

Question. Which of the follow group 15 element forms metallic bonds in elemental state ?
(A) As
(B) P
(C) Sb
(D) Bi

Question. Which of the following oxides is neutral ?
(A) N₂O₃
(B) N₂O₄
(C) N₂O₅
(D) N₂O

Question. Which of the following has the highest pπ – pπ bonding tendency ?
(A) N
(B) P
(C) As
(D) Sb

Question. Elements of group-15 form compounds in +5 oxidation state.
However, bismuth forms only one well characterised compound in +5 oxidation state. The compound is
(A) Bi₂O₅
(B) BiF₅
(C) BiCl₅
(D) Bi2S₅

Question. Zinc on reaction with dilute HNO₃ gives x and zinc on reaction with concentrated HNO₃ gives y. Identify x and y.
(A) x = NO₂ , y = N₂O
(B) x = N₂O , y = NO
(C) x = NO , y = NO₂
(D) x = N₂O , y = NO₂

Question. In Haber’s process for the manufacture of NH₃ :
(A) finely divided nickel is used as a catalyst
(B) finely divided iron is used as a catalyst
(C) finely divided molybdenum is used as a catalyst
(D) no catalyst is necessary

Question. Which of the following statement is incorrect for group 15 elements ?
(A) Order of ionization enthalpies is Δ_iH₁ < Δ_iH₂ < Δ_iH₃
(B) The boiling point and melting point increases from top to bottom in the group
(C) Dinitrogen is a gas while all others are solids
(D) All statements are correct

Question. Ammonia on reaction with hypochlorite anion can form :
(A) NO
(B) N₂H₄
(C) NH₄Cl
(D) Both (B) and (C)

Question. Which of the following is incorrect for white and red phosphorus ?
(A) They are both soluble in CS₂
(B) They can be oxidised by heating in air
(C) They consist of the same kind of atoms
(D) They can be converted into one another

Question. The shape of ammonia molecule is
(A) tetrahedral
(B) pyramidal
(C) planar triangle
(D) octahedral

Question. Nitrogen forms N₂, but phosphorus is converted into P₄ from P, the reason is
(A) Triple bond is present between phosphorus atom
(B) p_π – p_π bonding is strong
(C) p_π – p_π bonding is weak
(D) Multiple bond is formed easily

Question. In which the NH₃ is not used ?
(A) Cold storage
(B) Anaesthetic
(C) Manufacture of rayon and plastic
(D) None of these

Question. Which one has the lowest boiling point ?
(A) NH₃
(B) PH₃
(C) AsH₃
(D) SbH₃

Question. Ammonia is generally manufactured for fertilizers by the reaction
(A) 2NH₄Cl + Ca(OH)₂ → CaCl₂ + 2H₂O + 2NH₃
(B) By passing an electric discharge in a mixture of N₂ and H₂
(C) By passing a mixture of N₂ and H₂ under high pressure and moderate temperature over a catalyst
(D) None of these

Question. PCl₅ is possible but NCl₅ does not exist :
(A) in N, d-sub-shell is absent
(B) ionization energy of N is very high
(C) it does not like Cl
(D) None of these

Question. Nitrogen dioxide cannot be obtained by heating :
(A) KNO₃
(B) Pb(NO₃)₂
(C) Cu(NO₃)₂
(D) AgNO₃

Question. The bonds present in N₂O₅ are :
(A) only ionic
(B) covalent and coordinate
(C) only covalent
(D) covalent and ionic

Question. Which of the following shows nitrogen with its increasing order of oxidation number?
(A) NO < N₂O < NO₂ < NO₃^– < NH₄⁺
(B) NH₄⁺ < N₂O < NO₂ < NO₃^– < NO
(C) NH₄⁺ < N₂O < NO < NO₂ < NO₃^–
(D) NH₄⁺ < NO < N₂O < NO₂ < NO₃^–

Question. In which one of the following oxides of nitrogen, one nitrogen atom is not directly linked to oxygen?
(A) NO
(B) N₂O₄
(C) N₂O
(D) N₂O₃

Question. Which of the following oxides of nitrogen reacts with FeSO₄ to form a dark brown compound
(A) N₂O
(B) NO
(C) NO₂
(D) N₂O₃

Question. When ammonia is heated with cupric oxide, a molecule of ammonia will
(A) gain 3 electrons
(B) lose 3 electrons
(C) gain 2 electrons
(D) lose 2 electrons

Question. Which of the following can be used as an anaesthesia ?
(A) N₂O
(B) NO
(C) NCl₃
(D) NO₂

Question. Which of the following statements is not correct for nitrogen?
(A) Its electronegativity is very high
(B) d-orbitals are available for bonding
(C) It is a typical non-metal
(D) Its molecular size is small

Question. Which of the following oxides of nitrogen is a coloured gas?
(A) N₂O
(B) NO
(C) N₂O₅
(D) NO₂

Question. The catalyst used in the manufacture of HNO₃ by Ostwald’s process is :
(A) platinum gauze
(B) vanadium pentoxide
(C) finely divided nickel
(D) platinum black .

Question. What causes nitrogen to be chemically inert ?
(A) Multiple bond formation in the molecule
(B) Absence of bond polarity
(C) Short internuclear distance
(D) High bond energy

Question. Concentrated nitric acid, upon long standing, turns yellow brown due to the formation of
(A) NO
(B) NO₂
(C) N₂O
(D) N₂O₄

Question. Collectively the elements of group 15 are called –
(A) pnicogens
(B) pnicopens
(C) nicopen
(D) None of these

Question. What will be the A and B in the following equations.

(A) A = Excess, B = Excess
(B) A = Limited, B = Excess
(C) A = Excess, B = Limited
(D) A = Limited, B = Limited

Question. Which of the following is the strongest reducing agent ?
(A) NH₃
(B) PH₃
(C) BiH₃
(D) SbH₃

Question. The p-block element of group 15 that forms predominantly basic oxide is
(A) N
(B) P
(C) As
(D) Bi

Question. Which of the following element will form acidic oxides of type E₂O₃?
(A) As
(B) Sb
(C) Bi
(D) P

Question. Which of the following elements does not form stable diatomic molecules ?
(A) Iodine
(B) Phosphorus
(C) Nitrogen
(D) Oxygen

Question. Which of the following trihalide is unstable?
(A) NF₃`
(B) AsCl₃
(C) SbBr₃
(D) NCl₃

ASSERTION AND REASON BASED MCQs 

Directions: In the following questions, A statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as.
(A) Both A and R are true and R is the correct explanation of A
(B) Both A and R are true but R is NOT the correct explanation of A
(C) A is true but R is false
(D) A is false and R is True

Question. Assertion (A): H₂O a liquid and H₂S a gas.
Reason (R): Water molecules are held by H-bonds while in H₂S molecules no such interactions are present between molecules.

Question. Assertion (A): NaCl reacts with concentrated H₂SO₄ to give colourless fumes with pungent smell. But on adding MnO₂ the fumes become greenish yellow.
Reason (R): MnO₂ oxidises HCl to chlorine gas which is greenish yellow.

Question. Assertion (A): N₂ is less reactive than P4.
Reason (R): Nitrogen has more electron gain enthalpy than phosphorus.

Question. Assertion (A): Both rhombic and monoclinic sulphur exist as S8 but oxygen exists as O₂.
Reason (R): Oxygen forms pp-pp multiple bond due to small size and small bond length but pp-pp bonding is not possible in sulphur.

Question. Assertion (A): HNO₃ makes iron passive.
Reason (R): HNO₃ forms a protective layer of ferric nitrate on the surface of iron.

Question. Assertion(A): Helium diffuses through most commonly used laboratory materials.
Reason(R): This gas has a very low melting point.

Question. Assertion (A): SF₆ cannot be hydrolysed but SF₄ can be.
Reason (R): Six atoms in SF₆ prevent the attack of H₂O on sulphur atom of SF₆. 

Question. Assertion (A): HI cannot be prepared by the reaction of KI with concentrated H₂SO₄.
Reason (R): HI has lowest H–X bond strength among halogen acids.

Question. Assertion (A): Bismuth forms only one well characterised compound in +5 oxidation state.
Reason (R): Elements of group-15 form compounds in +5 oxidation state.

Question. Assertion (A): F₂ has lower bond dissociation energy than Cl₂.
Reason (R): Flourine is more electronegative than chlorine.

Question. Assertion (A): Helium used in diving apparatus.
Reason (R): Helium is very less soluble in blood.

Question. Assertion(A): Group 18 gases exhibit very high ionisation enthalpy.
Reason (R): They have a stable electronic configuration. 

Question. Assertion (A): F₂ is a strong oxidizing agent.
Reason (R): Electron gain enthalpy of fluorine is less negative. 

Question. Assertion (A): NaCl reacts with concentrated H₂SO₄ to give colourless fumes with pungent smell. But on adding MnO₂ the fumes become greenish yellow.
Reason (R): MnO₂ oxidises HCl to chlorine gas which is greenish yellow 

Question. Assertion(A): The noble gases are inactive.
Reason(R): These gases have a closed shell structure. 

Question. Assertion (A): F₂ has lower reactivity.
Reason (R): F-F bond has low Δbond Ho.

CASE-BASED MCQs

I. Read the passage given below and answer the following questions:

In spite of the predictions of stable noble gas compounds since at least 1902, unsuccessful attempts at their synthesis gave rise to the widely held opinion that noble gases are not only noble but also inert. It was not until 1962 that this dogma was shattered when Bartlett in Canada published the first stable noble gas compound XePtF6. This discovery triggered a worldwide frenzy in this area, and within a short time span many new xenon, radon, and krypton compounds were prepared and characterized. The recent discoveries show the ability of xenon to act as a ligand . The discovery by Seppelt’s group that more than one xenon atom can attach itself to a metal center which in the case of gold leads to surprisingly stable Au- Xe bonds. The bonding in [AuXe4]²⁺ involves 4 Xe ligands attached by relatively strong bonds to a single Au(II) center in a square planar arrangement with a Xe-Au bond length of about 274 pm This discovery provides not only the first example of multiple xenon ligands but also represents the first strong metal – xenon bond.

Question. Xe is a ___________ ligand
(A) ambidentate
(B) bidantate
(C) unidentate
(D) hexadentate

Question. Hybridisation shown by Au in [AuXe4]²⁺ is:
(A) sp3
(B) sp3d
(C) sp3d2
(D) sp2

Question. Compounds of noble gases except _______ are known.
(A) Krypton
(B) Radon
(C) Helium
(D) Xenon

Question. In the complex ion [AuXe4]²⁺, Xe acts as:
(A) central atom
(B) ligand
(C) chelating agent
(D) electrophile

II. Read the passage given below and answer the following questions:

In the last 10 years much has been learned about the molecular structure of elemental sulfur. lt is now known that many different types of rings are sufficiently metastable to exist at room temperature for several days. It is known that at high temperature, the equilibrium composition allows for a variety of rings and chains to exist in comparable concentration, and it is known that at the boiling point and above, the vapor as well as the liquid contains small species with three, four, and five atoms. The sulfur atom has the same number of valence electrons as oxygen. Thus, sulfur atoms S₂ and S₃ have physical and chemical properties analogous to those of oxygen and ozone. S₂ has a ground state of 38 σ3s²σ*3s²σ3pz²π3px 2 = p3py²π*3px¹ = π*3py¹. S3 , thiozone has a wellknown uv spectrum, and has a bent structure, analogous to its isovalent molecules 03, SO2, and S20. The chemistry of the two elements, sulphur and oxygen, differs because sulfur has a pronounced tendency for catenation. The most frequently quoted explanation is based on the electron structure of the atom. Sulfur has low-lying unoccupied 3d orbitals, and it is widely believed that the 4s and 3d orbitals of sulfur participate in bonding in a manner similar to the participation of 2s and 2p orbitals in carbon. 

In the following questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.

(A) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(B) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(C) Assertion is correct statement but reason is wrong statement.
(D) Assertion is wrong statement but reason is correct statement.

Question. Assertion (A): Thiozone has bent structure like ozone.
Reason (R): Ozone has a lone pair which makes the molecule bent.
Ans. Option (B) is correct.

Question. Assertion (A): Sulphur has a greater tendency for catenation than oxygen.
Reason (R): 3d and 4s orbitals of Sulphur have same energy.

Question. Assertion (A): Sulphur belongs to same group in the periodic table as oxygen.
Reason (R): S₂ has properties analogous to O₂.

Ques tion. Assertion (A): S₂ is paramagnetic in nature
Reason (R): The electrons in p*3px and p*3py orbitals in S₂ are unpaired.

III. Read the given passage and answer the questions (i) to (iv) that follow:

The halogens have the smallest atomic radii in their respective periods. The atomic radius of fluorine is extremely small. All halogens exhibit –1 oxidation state. They are strong oxidising agents and have maximum negative electron gain enthalpy. Among halogens, fluorine shows anomalous behaviour in many properties. For example electronegativity and ionisation enthalpy are higher for fluorine than expected whereas bond dissociation enthalpy, m.p. and b.p. and electron gain enthalpy are quite lower than expected. Halogens react with hydrogen to give hydrogen halides (HX) and combine amongst themselves to form a number of compounds of the type XX’, XX’₃, XX’₅ and XX’₇ called inter-halogens.

Question. Why fluorine shows anomalous behaviour as compared to other halogens?
Answer: (i) It has smallest in size.
(ii) Very high electronegativity.
(iii) Absence of d-orbitals.
(iv) dissociation enthalpy in molecular form is least. 

Question. What are the sizes of X and X’ in the interhalogen compounds?
Answer: Size of X is greater than X’.

Question. Why halogens have maximum negative electron gain enthalpy?
Answer: Halogens have only seven electrons in their valence shell. So they require only one electron to attain a noble gas configuration.Hence they have maximum electron gain
enthalpy.

Question. Arrange the hydrogen halides (HF to HI) in the decreasing order of their reducing character.
Answer: HI > HBr > HCl > HF

Question. Why fluorine is a stronger oxidizing agent than chlorine?
Answer: Because fluorine has greater E° value (2.87V) than chlorine (1.36V).