Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven The p-Block Elements

Explain why the stability of oxoacids of chlorine increases in the order given below:

HClO < HClO₂ < HClO₃ < HClO₄

In PCl₅ , phosphorus is in sp₃d hybridised state but all its five bonds are not equivalent. Justify your answer with reason.

Why is nitric oxide paramagnetic in gaseous state but the solid obtained on cooling it is diamagnetic?

In reaction with Cl₂ , phosphorus forms two types of halides ‘A’ and ‘B’. Halide A is yellowish-white powder but halide ‘B’ is colourless oily liquid. Identify A and B and write the formulas of their hydrolysis products.

In the ring test of NO₃^-  ion, Fe₂⁺ ion reduces nitrate ion to nitric oxide, which combines with Fe2 + (aq) ion to form brown complex. Write the reactions involved in the formation of brown rings.

P₄O₆ reacts with water according to equation P₄O₆ + 6H₂O→ 4H₃PO₃. Calculate the volume of 0.1 M NaOH solution required to neutralise the acid formed by dissolving 1.1 g of P₄O₆ in H₂O.

White phosphorus reacts with chlorine and the product hydrolyses in the presence of water. Calculate the mass of HCl obtained by the hydrolysis of the product formed by the reaction of 62 g of white phosphorus with chlorine in the presence of water

Name three oxoacids of nitrogen. Write the disproportionation reaction of that oxoacid of nitrogen in which nitrogen is in +3 oxidation state.

Nitric acid forms an oxide of nitrogen on reaction with P₄O₁₀. Write the reaction involved. Also write the resonating structures of the oxide of nitrogen formed.

Phosphorus has three allotropic forms — (i) white phosphorus (ii) red phosphorus and (iii) black phosphorus. Write the difference between white and red phosphorus since their structure and reactivity.

Give an example to show the effect of concentration of nitric acid on the formation of oxidation products.

PCl₅ reacts with finely divided silver on heating and a white silver salt is obtained, which dissolves on adding excess aqueous NH₃ solution. Write the reactions involved to explain what happens.

Phosphorus forms several oxoacids. Out of these oxoacids phosphinic acid has strong reducing properties. Write its structure and write a reaction showing its reducing behaviour

Write a balanced chemical equation for the reaction showing catalytic oxidation of NH₃ by atmospheric oxygen.

An amorphous solid “A” burns in air to form a gas “B” which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolourises acidified aqueous KMnO₄ solution and reduces Fe₃⁺  to Fe₂⁺ . Identify the solid “A” and the gas “B” and write the reactions involved.

On heating lead (II) nitrate gives a brown gas “A”. The gas “A” on cooling changes to colourless solid “B”. Solid “B” on heating with NO changes to a blue solid ‘C’. Identify ‘A’, ‘B’ and ‘C’ and write reactions involved and draw the structures of ‘B’ and ‘C’.

Match the species given in Column I with the shape given in Column II and mark the correct option.

Assertion : HI cannot be prepared by the reaction of KI with concentrated H₂SO₄

Reason : HI has lowest H–X bond strength among halogen acids

(i) Both assertion and reason are correct statements, and reason is the correct explanation of the assertion. 

(ii) Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.

(iii) Assertion is correct, but reason is wrong statement. 

(iv) Assertion is wrong but reason is correct statement. 

(v) Both assertion and reason are wrong statements.

Assertion : Both rhombic and monoclinic sulphur exist as S₈ but oxygen exists as O₂ . 

Reason : Oxygen forms pπ – pπ multiple bonds due to small size and small bond length Pπ- Pπ  bonding is not possible in sulphur.

(i) Both assertion and reason are correct statements, and reason is the correct explanation of the assertion. 

(ii) Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.

(iii) Assertion is correct, but reason is wrong statement. 

(iv) Assertion is wrong but reason is correct statement. 

(v) Both assertion and reason are wrong statements.

Assertion : NaCl reacts with concentrated H₂SO₄ to give colourless fumes with pungent smell. But on adding MnO₂ the fumes become greenish yellow. 

Reason : MnO₂ oxidises HCl to chlorine gas which is greenish yellow.

(i) Both assertion and reason are correct statements, and reason is the correct explanation of the assertion. 

(ii) Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.

(iii) Assertion is correct, but reason is wrong statement. 

(iv) Assertion is wrong but reason is correct statement. 

(v) Both assertion and reason are wrong statements.

Assertion : SF₆ cannot be hydrolysed but SF₄ can be. 

Reason : Six F atoms in SF₆ prevent the attack of H₂O on sulphur atom of SF₆

(i) Both assertion and reason are correct statements, and reason is the correct explanation of the assertion. 

(ii) Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.

(iii) Assertion is correct, but reason is wrong statement. 

(iv) Assertion is wrong but reason is correct statement. 

(v) Both assertion and reason are wrong statements.

Which of the following acids forms three series of salts? 

(i) H₃PO₂

(ii) H₃BO₃ 

(iii) H₃PO₄

(iv) H₃PO₃

On heating ammonium dichromate and barium azide separately we get 

(i) N₂ in both cases 

(ii) N₂ with ammonium dichromate and NO with barium azide 

(iii) N₂O with ammonium dichromate and N₂ with barium azide 

(iv) N₂O with ammonium dichromate and NO₂ with barium azide

Which of the following are peroxoacids of sulphur? 

(i) H₂SO₅ and H₂S₂O₈

(ii) H₂SO₅ and H₂S₂O₇

(iii) H₂S₂O₇ and H₂S₂O₈

(iv) H₂S₂O₆ and H₂S₂O₇

In the preparation of compounds of Xe, Bartlett had taken O₂⁺ PtF₆⁻  as a base compound. This is because 

(i) Both O₂ and Xe have the same size. 

(ii) Both O₂ and Xe have the same electron gain enthalpy. 

(iii) Both O₂ and Xe have almost the same ionisation enthalpy. 

(iv) Both O₂ and Xe are gases.

Which of the following is an isoelectronic pair? 

(i) ICl₂ , ClO₂

(ii) BrO₂^-  , BrF₂

(iii) ClO₂ , BrF

(iv) CN^- , O₃

Which of the following options are not in accordance with the property mentioned against them?

(i) F₂ >  Cl₂ >  Br₂ > I₂                              Oxidising power. 

(ii) MI  >  MBr  >  MCl  >  MF                  Ionic character of metal halide. 

(iii) F₂ >  Cl₂ >  Br₂ > I₂                            Bond dissociation enthalpy. 

(iv) HI  <  HBr  <  HCl  <  HF                   Hydrogen-halogen bond strength.

Which of the following statements are correct for SO₂ gas? 

(i) It acts as a bleaching agent in moist conditions. 

(ii) It’s molecule has linear geometry. 

(iii) It’s dilute solution is used as disinfectant. 

(iv) It can be prepared by the reaction of dilute H₂SO₄ with metal sulphide.

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

(i) As₂O₃ < SiO₂ < P₂O₃ < SO₂               Acid strength. 

(ii) AsH₃ < PH₃ < NH₃                             Enthalpy of vapourisation. 

(iii) S< O < Cl <  F                                    More negative electron gain enthalpy. 

(iv) H₂O  > H₂S  > H₂Se  > H₂Te             Thermal stability.

Which of the following statements are correct? 

(i) S–S bond is present in H₂S₂O₆. 

(ii) In peroxosulphuric acid H₂SO₄ sulphur is in +6 oxidation state. 

(iii) Iron powder along with Al₂O₃ and K₂O is used as a catalyst in the preparation of NH₃ by Haber’s process. 

(iv) Change in enthalpy is positive for the preparation of SO₃ by catalytic oxidation of SO₂.

Which of the following statements are true? 

(i) Only type of interactions between particles of noble gases are due to weak dispersion forces. 

(ii) Ionisation enthalpy of molecular oxygen is very close to that of xenon. 

(iii) Hydrolysis of XeF₆ is a redox reaction. 

(iv) Xenon fluorides are not reactive.

In a cyclotrimetaphosphoric acid molecule, how many single and double bonds are present? 

(i) 3 double bonds; 9 single bonds 

(ii) 6 double bonds; 6 single bonds 

(iii) 3 double bonds; 12 single bonds 

(iv) Zero double bonds; 12 single bonds

Which of the following elements can be involved in p\pi --d\pi  bonding? 

(i) Carbon 

(ii) Nitrogen 

(iii) Phosphorus 

(iv) Boron

Which of the following pairs of ions are isoelectronic and isostructural? 

(i) CO₃^2-  , NO₃^- 

(ii) ClO₃^-  , CO₃^2- 

(iii) SO₃^2- , NO₃^- 

(iv) ClO₃^-  , SO₃^2- 

Affinity for hydrogen decreases in the group from fluorine to iodine. Which of the halogen acids should have highest bond dissociation enthalpy? 

(i) HF

(ii) HCl

(iii) HBr 

(iv) HI

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

Compound NH₃ PH₃ AsH₃ SbH₃ 

Δdiss(E---H)/kJ mol--1 389          322       297         255

(i) NH₃

(ii) PH₃

(iii) AsH₃

(iv) SbH₃

On heating with concentrated NaOH solution in an inert atmosphere of CO₂, white phosphorus gives a gas. Which of the following statements is incorrect about the gas? 

(i) It is highly poisonous and smells like rotten fish. 

(ii) It’s solution in water decomposes in the presence of light. 

(iii) It is more basic than NH₃.

(iv) It is less basic than NH₃.

Strong reducing behaviour of H₃PO₂ is due to 

(i) Low oxidation state of phosphorus 

(ii) Presence of two –OH groups and one P–H bond

(iii) Presence of one –OH group and two P–H bonds 

(iv) High electron gain enthalpy of phosphorus

On heating lead nitrate forms oxides of nitrogen and lead. The oxides formed are ______. 

(i) N₂O, PbO

(ii) NO₂, PbO 

(iii) NO, PbO 

(iv) NO, PbO₂

Which of the following elements does not show allotropy? 

(i) Nitrogen 

(ii) Bismuth 

(iii) Antimony 

(iv) Arsenic

Which of the following statements is wrong? 

(i) Single N–N bond is stronger than the single P–P bond. 

(ii) PH₃ can act as a ligand in the formation of coordination compound with transition elements. 

(iii) NO₂ is paramagnetic in nature. 

(iv) Covalency of nitrogen in N₂O₅ is four

A brown ring is formed in the ring test for NO₃^- ion. It is due to the formation of 

(i) [Fe(H₂O)₅(NO)]²⁺ 

(ii) FeSO₄ .NO₂

(iii) [Fe(H₂O)₄(NO)₂]²⁺ 

(iv) FeSO₄.HNO₃

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 

(i) Bi₂O₅ 

(ii) BiF₅ 

(iii) BiCl₅

(iv) Bi₂S₅

In the preparation of HNO₃, we get NO gas by catalytic oxidation of ammonia. The moles of NO produced by the oxidation of two moles of NH₃ will be______. 

(i) 2 

(ii) 3 

(iii) 4 

(iv) 6

The oxidation state of central atom in the anion of compound NaH₂PO₂ will be ______.

(i) +3 

(ii) +5 

(iii) +1 

(iv) –3

Which of the following is not tetrahedral in shape? 

(i) NH₄⁺ 

(ii) SiCl₄ 

(iii) SF₄ 

(iv) SO₄²⁻

Hot conc. H₂SO₄ acts as moderately strong oxidising agent. It oxidises both metals and nonmetals. Which of the following element is oxidised by conc. H₂SO₄ into two gaseous products?

(i) Cu

(ii) S

(iii) C 

(iv) Zn

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 trihalide is formed. In this process the oxidation state of nitrogen changes from _________. 

(i) – 3 to +3 

(ii) – 3 to 0 

(iii) – 3 to +5 

(iv) 0 to – 3

In solid state PCl₅ is a _________. 

(i) Covalent solid 

(ii) Octahedral structure 

(iii) Ionic solid with [PCl₆]⁺   octahedral and [PCl₄]⁻  tetrahedral

(iv) Ionic solid with [PCl₄]⁺  tetrahedral and [PCl₆]⁻  octahedral

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

(i) ClO₄^-  >  IO₄^-  >  BrO₄^- 

(ii) IO₄^-  >  BrO₄^-  >  ClO₄^-  

(iii) BrO₄^-  >  IO₄^-  >  ClO₄^-  

(iv) BrO₄^-  >  ClO₄^-  >  IO₄^- 

If chlorine gas is passed through hot NaOH solution, two changes are observed in the oxidation number of chlorine during the reaction. These are ________ and _________. 

(i) 0 to +5 

(ii) 0 to +3 

(iii) 0 to –1 

(iv) 0 to +1

Which of the following is correct for P₄ molecule of white phosphorus? 

(i) It has 6 lone pairs of electrons. 

(ii) It has six P–P single bonds. 

(iii) It has three P–P single bonds. 

(iv) It has four lone pairs of electrons.

Which of the following statements are correct? 

(i) Among halogens, the radius ratio between iodine and fluorine is maximum. 

(ii) Leaving the F—F bond, all halogens have weaker X—X bonds than X—X'bonds in interhalogens. 

(iii) Among interhalogen compounds maximum number of atoms are present in iodine fluoride. 

(iv) Interhalogen compounds are more reactive than halogen compounds.

Which of the following statements are correct? 

(i) All the three N—O bond lengths in HNO3 are equal. 

(ii) All P—Cl bond lengths in PCl₅ molecule in gaseous state are equal. 

(iii) P₄ molecule in white phosphorus have angular strain therefore white phosphorus is very reactive. 

(iv) PCl is ionic in solid state in which cation is tetrahedral and anion is octahedral.

In which of the following reactions conc. H₂SO₄ is used as an oxidising reagent? 

(i) CaF₂ + H₂SO₄ →CaSO₄ +  2HF 

(ii) 2HI  + H₂SO4 → I₂ +  SO₂ +  2H₂O

(iii) Cu  +  2H₂SO₄ →CuSO₄ +  SO₂ + 2H₂O 

(iv) NaCl  + H₂SO₄ → NaHSO₄ +  HCl

Match List – I with List – II.

    List – I                            List – II

(A) Siderite                           (i) Cu

(B) Calamine                        (ii) Ca

(C) Malachite                       (iii) Fe

(D) Cryolite                          (iv) Al

                                            (v) Zn

Choose the correct answer from the options given below

Ceric ammonium nitrate and CHCl₃/alc. KOH are used for the identification of functional groups present in…………. and……………respectively.

Match List-I with List-II.

List – I                                                                               List – II

(A)  Sucrose                                                                     (i) β-D-Galactose and β-D-Glucose

(B)  Lactose                                                                     (ii) α-D-Glucose and β-D-Fructose

(C) Maltose                                                                     (iii) α-D-Glucose and α-D-Glucose

Choose the correct answer from the options given below:

A 2.0g sample containing MnO₂ is treated with HCl liberating Cl₂. The Cl₂ gas is passed into a solution of Kl and 60.0mL of 0.1M Na₂S₂O₃ is required to titrate the liberated iodine. The percentage of MnO₂ in the sample is_______. (Nearest integer)

 [Atomic masses (in u) Mn = 55; Cl = 35.5; O = 16, I = 127, Na = 23, K = 39, S = 32]

If the work function of a metal is 6.63 × 10^-19J, the maximum wavelength of the photon required to remove a photoelectron from the metal is _______nm. (Nearest integer)

[Given h = 6.63 × 10^-34 Js, and c = 3 × 10⁸ ms^-1]

4.0 L of an ideal gas is allowed to expand isothermally into vacuum until the total volume is 20L. The amount of heat absorbed in this expansion is _________L atm.

The vapour pressure of two volatile liquid A and B at 25°C are 50 Torr and 100 Torr, respectively. If the liquid mixture contains 0.3 mole fraction of A, then the mole fraction of liquid B in the vapour phase is $\frac{x}{17}.$  The value of x is____________.

The solubility product of a sparingly soluble salt A₂X₃ is 1.1 × 10^-23. If specific conductance of the solution is 3 × 10^-1, the limiting molar conductivity of the solution is x × 10^-3 S m² mol^-1. The value of x is_________.

For a first order reaction A®B, the rate constant, k = 5.5 × 10^-14s^-1. The time required for 67% completion of reaction is x × 10^-1 times the half life of reaction. The value of x is ________ (Nearest integer)

           (Given : log 3 = 0.4771)

In the estimation of bromine, 0.5g of an organic compound gave 0.40g of silver bromide. The percentage of bromine in the given compound is____________% (Nearest integer)

           (Relative atomic masses of Ag and Br are 18 u and 80 u, respectively).