NCERT Exemplar solutions for केमिस्ट्री इग्ज़ेम्प्लार [अंग्रेजी} कक्षा १२ chapter 7 - The p-block Elements [Latest edition]

On addition to conc. \[\ce{H2SO4}\] to a chloride salt, colourless fumes are evolved but in the case of an iodide salt, violet flames come out. This is because ______.

In qualitative analysis when \[\ce{H2S}\] is passed through an aqueous solution of salt acidified with dil. \[\ce{HCl}\], a black precipitate is obtained. On boiling the precipitate with dil. \[\ce{HNO3}\], it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives ______.

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

Which of the following elements can be involved in pπ – dπ bonding?

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

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

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

On heating with concentrated \[\ce{NaOH}\] solution in an inert atmosphere of \[\ce{CO2}\], white phosphorus gives a gas. Which of the following statement is incorrect about the gas?

Which of the following acids forms three series of salts?

Strong reducing behaviour of \[\ce{H3PO2}\] is due to ______.

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

Which of the following elements does not show allotropy?

Maximum covalency of nitrogen is ______.

Which of the following statements is wrong?

A brown ring is formed in the ring test for \[\ce{NO3^{-}}\] ion. It is due to the formation of ______.

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 ______.

On heating ammonium dichromate and barium azide separately we get ______.

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 ______.

The oxidation state of central atom in the anion of compound \[\ce{NaH2PO2}\] will be ______.

Which of the following is not tetrahedral in shape?

Which of the following are peroxoacids of sulphur?

Hot conc. \[\ce{H2SO4}\] acts as the moderately strong oxidising agent. It oxidises both metals and non-metals. Which of the following element is oxidised by conc. \[\ce{H2SO4}\] into two gaseous products?

A black compound of manganese reacts with a halogen acid to give greenish-yellow gas. When excess of this gas reacts with \[\ce{NH3}\] an unstable trihalide is formed. In this process the oxidation state of nitrogen changes from ______.

In the preparation of compounds of Xe, Bartlett had taken \[\ce{O^{+}_2 Pt F^{-}_6}\] as a base compound. This is because ______.

In solid state \[\ce{PCl5}\] is a ______.

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

Which of the following is isoelectronic pair?

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

(i) 0 to +5

(ii) 0 to +3

(iii) 0 to –1

(iv) 0 to +1

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

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, radius ratio between iodine and fluorine is maximum.

(ii) Leaving F – F bond, all halogens have weaker X – X bond than X – X' bond 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 for \[\ce{SO2}\] gas?

(i) It acts as 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 \[\ce{H2SO4}\] with metal sulphide.

Which of the following statements are correct?

(i) All the three N – O bond lengths in \[\ce{HNO3}\] are equal.

(ii) All P – Cl bond lengths in \[\ce{PCl5}\] molecule in gaseous state are equal.

(iii) \[\ce{P4}\] molecule in white phosphorus have angular strain therefore white phosphorus is very reactive.

(iv) \[\ce{PCl}\] is ionic in solid state in which cation is tetrahedral and anion is octahedral.

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

Which of the following statements are correct?

(i) S – S bond is present in \[\ce{H2S2O6}\].

(ii) In peroxosulphuric acid \[\ce{(H2SO5)}\] sulphur is in +6 oxidation state.

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

(iv) Change in enthalpy is positive for the preparation of \[\ce{SO3}\] by catalytic oxidation of \[\ce{SO2}\].

Which of the following statements are correct?

(i) \[\ce{CaF2 + H2SO4 -> CaSO4 + 2HF}\]

(ii) \[\ce{2HI + H2SO4 -> I2 + SO2 + 2H2O}\]

(iii) \[\ce{Cu + 2H2SO4 -> CuSO4 + SO2 + 2H2O}\]

(iv) \[\ce{Nacl + H2SO4 -> NaHSO4 + HCl}\]

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 the preparation of \[\ce{H2SO4}\] by Contact Process, why is \[\ce{SO3}\] not absorbed directly in water to form \[\ce{H2SO4}\]?

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

Write the structure of pyrophosphoric acid.

PH₃ forms bubbles when passed slowly in water but NH₃ dissolves. Explain why?

In \[\ce{PCl5}\], 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?

Give reason to explain why ClF₃ exists but FCl₃ does not exist.

Out of \[\ce{H2O}\] and \[\ce{H2S}\], which one has higher bond angle and why?

SF₆ is known but SCl₆ is not. Why?

On reaction with \[\ce{Cl2}\], 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 \[\ce{NO^{-}3}\] ion, \[\ce{Fe^{2+}}\] ion reduces nitrate ion to nitric oxide, which combines with  \[\ce{Fe^{2+} (aq)}\] ion to form brown complex. Write the reactions involved in the formation of brown ring.

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

\[\ce{HClO < HClO2 < HClO3 < HClO4}\]

Explain why ozone is thermodynamically less stable than oxygen.

\[\ce{P4O6}\] reacts with water according to equation \[\ce{P4O6 + 6H2O -> 4H3PO3}\]. Calculate the volume of 0.1 M NaOH solution required to neutralise the acid formed by dissolving 1.1 g of \[\ce{P4O6}\] in \[\ce{H2O}\].

White phosphorus reacts with chlorine and the product hydrolyses in the presence of water. Calculate the mass of \[\ce{HCl}\] 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 on the basis of their structure and reactivity.

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

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

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

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

Match the formulas of oxides given in Column I with the type of oxide given in Column II and mark the correct option.

Match the items of Columns I and II and mark the correct option.

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

Match the items of Columns I and II and mark the correct option.

Assertion: N₂ is less reactive than P₄.

Reason: Nitrogen has more electron gain enthalpy than phosphorus.

Assertion: \[\ce{HNO3}\] makes iron passive.

Reason: \[\ce{HNO3}\] forms a protective layer of ferric nitrate on the surface of iron.

Assertion: \[\ce{HI}\] cannot be prepared by the reaction of KI with concentrated \[\ce{H2SO4}\]

Reason: \[\ce{HI}\] has lowest \[\ce{H - X}\] bond strength among halogen acids.

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 but pπ – pπ bonding is not possible in sulphur.

Assertion: \[\ce{NaCl}\] reacts with concentrated \[\ce{H2SO4}\] to give colourless fumes with pungent smell. But on adding \[\ce{MnO2}\] the fumes become greenish yellow.

Reason: \[\ce{MnO2}\] oxidises \[\ce{HCl}\] to chlorine gas which is greenish yellow.

Assertion: \[\ce{SF6}\] cannot be hydrolysed but \[\ce{SF4}\] can be.

Reason: Six \[\ce{F}\] atoms in \[\ce{SF6}\] prevent the attack of \[\ce{H2O}\] on sulphur atom of \[\ce{SF6}\].

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 \[\ce{KMnO4}\] solution and reduces \[\ce{Fe^{3+}}\] to \[\ce{Fe^{2+}}\]. 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 also write reactions involved and draw the structures of ‘B’ and ‘C’.

On heating compound (A) gives a gas (B) which is a constituent of air. This gas when treated with 3 mol of hydrogen (H₂) in the presence of a catalyst gives another gas (C) which is basic in nature. Gas C on further oxidation in moist condition gives a compound (D) which is a part of acid rain. Identify compounds (A) to (D) and also give necessary equations of all the steps involved.