Chapter 7 The P-Block Elements

Question 1. On addition of conc. $H_2SO_4$ to a chloride salt, colourless fumes are evolved but in case of iodide salt, violet fumes come out. This is because

(i) $H_2SO_4$ reduces HI to $I_2$

(ii) HI is of violet colour

(iii) HI gets oxidised to $I_2$

(iv) HI changes to $HIO_3$

Question 2. In qualitative analysis when $H_2S$ is passed through an aqueous solution of salt acidified with dil. HCl, a black precipitate is obtained. On boiling the precipitate with dil. $HNO_3$, it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives _________.

(i) deep blue precipitate of $Cu(OH)_2$

(ii) deep blue solution of $[Cu(NH_3)_4]^{2+}$

(iii) deep blue solution of $Cu(NO_3)_2$

(iv) deep blue solution of $Cu(OH)_2 \cdot Cu(NO_3)_2$

Question 3. 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

Question 4. Which of the following elements can be involved in $p\pi–d\pi$ bonding?

(i) Carbon

(ii) Nitrogen

(iii) Phosphorus

(iv) Boron

Question 5. Which of the following pairs of ions are isoelectronic and isostructural?

(i) $CO_3^{2-}, NO_3^-$

(ii) $ClO_3^-, CO_3^{2-}$

(iii) $SO_3^{2-}, NO_3^-$

(iv) $ClO_3^-, SO_3^{2-}$

Question 6. 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

Question 7. Bond dissociation enthalpy of E—H (E = element) bonds is given below. Which of the compounds will act as strongest reducing agent?

(i) $NH_3$

(ii) $PH_3$

(iii) $AsH_3$

(iv) $SbH_3$

Question 8. On heating with concentrated NaOH solution in an inert atmosphere of $CO_2$, white phosphorus gives a gas. Which of the following statement is incorrect about the gas?

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

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

(iii) It is more basic than $NH_3$.

(iv) It is less basic than $NH_3$.

Question 9. Which of the following acids forms three series of salts?

(i) $H_3PO_2$

(ii) $H_3BO_3$

(iii) $H_3PO_4$

(iv) $H_3PO_3$

Question 10. Strong reducing behaviour of $H_3PO_2$ 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

Question 11. On heating lead nitrate forms oxides of nitrogen and lead. The oxides formed are ______.

(i) $N_2O$, PbO

(ii) $NO_2$, PbO

(iii) NO, PbO

(iv) NO, $PbO_2$

Question 12. Which of the following elements does not show allotropy?

(i) Nitrogen

(ii) Bismuth

(iii) Antimony

(iv) Arsenic

Question 13. Maximum covalency of nitrogen is ______________.

(i) 3

(ii) 5

(iii) 4

(iv) 6

Question 14. Which of the following statements is wrong?

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

(ii) $PH_3$ can act as a ligand in the formation of coordination compound with transition elements.

(iii) $NO_2$ is paramagnetic in nature.

(iv) Covalency of nitrogen in $N_2O_5$ is four.

Question 15. A brown ring is formed in the ring test for $NO_3^-$ ion. It is due to the formation of

(i) $[Fe(H_2O)_5 (NO)]^{2+}$

(ii) $FeSO_4.NO_2$

(iii) $[Fe(H_2O)_4(NO)_2]^{2+}$

(iv) $FeSO_4.HNO_3$

Question 16. 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) $Bi_2O_5$

(ii) $BiF_5$

(iii) $BiCl_5$

(iv) $Bi_2S_5$

Question 17. On heating ammonium dichromate and barium azide separately we get

(i) $N_2$ in both cases

(ii) $N_2$ with ammonium dichromate and NO with barium azide

(iii) $N_2O$ with ammonium dichromate and $N_2$ with barium azide

(iv) $N_2O$ with ammonium dichromate and $NO_2$ with barium azide

Question 18. In the preparation of $HNO_3$, we get NO gas by catalytic oxidation of ammonia. The moles of NO produced by the oxidation of two moles of $NH_3$ will be ______.

(i) 2

(ii) 3

(iii) 4

(iv) 6

Question 19. The oxidation state of central atom in the anion of compound $NaH_2PO_2$ will be ______.

(i) +3

(ii) +5

(iii) +1

(iv) –3

Question 20. Which of the following is not tetrahedral in shape?

(i) $NH_4^+$

(ii) $SiCl_4$

(iii) $SF_4$

(iv) $SO_4^{2–}$

Question 21. Which of the following are peroxoacids of sulphur?

(i) $H_2SO_5$ and $H_2S_2O_8$

(ii) $H_2SO_5$ and $H_2S_2O_7$

(iii) $H_2S_2O_7$ and $H_2S_2O_8$

(iv) $H_2S_2O_6$ and $H_2S_2O_7$

Question 22. Hot conc. $H_2SO_4$ acts as moderately strong oxidising agent. It oxidises both metals and nonmetals. Which of the following element is oxidised by conc. $H_2SO_4$ into two gaseous products?

(i) Cu

(ii) S

(iii) C

(iv) Zn

Question 23. A black compound of manganese reacts with a halogen acid to give greenish yellow gas. When excess of this gas reacts with $NH_3$ 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

Question 24. In the preparation of compounds of Xe, Bartlett had taken $O_2^+ Pt F_6^–$ as a base compound. This is because

(i) both $O_2$ and Xe have same size.

(ii) both $O_2$ and Xe have same electron gain enthalpy.

(iii) both $O_2$ and Xe have almost same ionisation enthalpy.

(iv) both Xe and $O_2$ are gases.

Question 25. In solid state $PCl_5$ is a _________.

(i) covalent solid

(ii) octahedral structure

(iii) ionic solid with $[PCl_6]^+$ octahedral and $[PCl_4]^–$ tetrahedra

(iv) ionic solid with $[PCl_4]^+$ tetrahedral and $[PCl_6]^–$ octahedra

Question 26. Reduction potentials of some ions are given below. Arrange them in decreasing order of oxidising power.

(i) $ClO_4^– > IO_4^– > BrO_4^–$

(ii) $IO_4^– > BrO_4^– > ClO_4^–$

(iii) $BrO_4^– > IO_4^– > ClO_4^–$

(iv) $BrO_4^– > ClO_4^– > IO_4^–$

Question 27. Which of the following is isoelectronic pair?

(i) $ICl_2, ClO_2$

(ii) $BrO_2^-, BrF_2^+$

(iii) $ClO_2, BrF$

(iv) $CN^–, O_3$

Question 28. 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

Question 29. Which of the following options are not in accordance with the property mentioned against them?

(i) $F_2 > Cl_2 > Br_2 > I_2$ Oxidising power.

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

(iii) $F_2 > Cl_2 > Br_2 > I_2$ Bond dissociation enthalpy.

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

Question 30. Which of the following is correct for $P_4$ 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.

Question 31. 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.

Question 32. Which of the following statements are correct for $SO_2$ 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 $H_2SO_4$ with metal sulphide.

Question 33. Which of the following statements are correct?

(i) All the three N—O bond lengths in $HNO_3$ are equal.

(ii) All P—Cl bond lengths in $PCl_5$ molecule in gaseous state are equal.

(iii) $P_4$ molecule in white phohsphorus have angular strain therefore white phosphorus is very reactive.

(iv) $PCl_5$ is ionic in solid state in which cation is tetrahedral and anion is octahedral.

Question 34. Which of the following orders are correct as per the properties mentioned against each?

(i) $As_2O_3 < SiO_2 < P_2O_3 < SO_2$ Acid strength.

(ii) $AsH_3 < PH_3 < NH_3$ Enthalpy of vapourisation.

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

(iv) $H_2O > H_2S > H_2Se > H_2Te$ Thermal stability.

Question 35. Which of the following statements are correct?

(i) S–S bond is present in $H_2S_2O_6$.

(ii) In peroxosulphuric acid ($H_2SO_5$) sulphur is in +6 oxidation state.

(iii) Iron powder along with $Al_2O_3$ and $K_2O$ is used as a catalyst in the preparation of $NH_3$ by Haber’s process.

(iv) Change in enthalpy is positive for the preparation of $SO_3$ by catalytic oxidation of $SO_2$.

Question 36. In which of the following reactions conc. $H_2SO_4$ is used as an oxidising reagent?

(i) $CaF_2 + H_2SO_4 \rightarrow CaSO_4 + 2HF$

(ii) $2HI + H_2SO_4 \rightarrow I_2 + SO_2 + 2H_2O$

(iii) $Cu + 2H_2SO_4 \rightarrow CuSO_4 + SO_2 + 2H_2O$

(iv) $NaCl + H_2SO_4 \rightarrow NaHSO_4 + HCl$

Question 37. 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 $XeF_6$ is a redox reaction.

(iv) Xenon fluorides are not reactive.

Question 38. In the preparation of $H_2SO_4$ by Contact Process, why is $SO_3$ not absorbed directly in water to form $H_2SO_4$?

Question 39. Write a balanced chemical equation for the reaction showing catalytic oxidation of $NH_3$ by atmospheric oxygen.

Question 40. Write the structure of pyrophosphoric acid.

Question 41. $PH_3$ forms bubbles when passed slowly in water but $NH_3$ dissolves. Explain why?

Question 42. In $PCl_5$, phosphorus is in $sp^3d$ hybridised state but all its five bonds are not equivalent. Justify your answer with reason.

Question 43. Why is nitric oxide paramagnetic in gaseous state but the solid obtained on cooling it is diamagnetic?

Question 44. Give reason to explain why $ClF_3$ exists but $FCl_3$ does not exist.

Question 45. Out of $H_2O$ and $H_2S$, which one has higher bond angle and why?

Question 46. $SF_6$ is known but $SCl_6$ is not. Why?

Question 47. On reaction with $Cl_2$, 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.

Question 48. In the ring test of $NO_3^–$ ion, $Fe^{2+}$ ion reduces nitrate ion to nitric oxide, which combines with $Fe^{2+}$ (aq) ion to form brown complex. Write the reactions involved in the formation of brown ring.

Question 49. Explain why the stability of oxoacids of chlorine increases in the order given below:

$HClO < HClO_2 < HClO_3 < HClO_4$

Question 50. Explain why ozone is thermodynamically less stable than oxygen.

Question 51. $P_4O_6$ reacts with water according to equation $P_4O_6 + 6H_2O \rightarrow 4H_3PO_3$. Calculate the volume of 0.1 M NaOH solution required to neutralise the acid formed by dissolving 1.1 g of $P_4O_6$ in $H_2O$.

Question 52. 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.

Question 53. Name three oxoacids of nitrogen. Write the disproportionation reaction of that oxoacid of nitrogen in which nitrogen is in +3 oxidation state.

Question 54. Nitric acid forms an oxide of nitrogen on reaction with $P_4O_{10}$. Write the reaction involved. Also write the resonating structures of the oxide of nitrogen formed.

Question 55. 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.

Question 56. Give an example to show the effect of concentration of nitric acid on the formation of oxidation product.

Question 57. $PCl_5$ reacts with finely divided silver on heating and a white silver salt is obtained, which dissolves on adding excess aqueous $NH_3$ solution. Write the reactions involved to explain what happens.

Question 58. 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.

Question 59. Match the compounds given in Column I with the hybridisation and shape given in Column II and mark the correct option.

Code :

(i) A (1) B (3) C (4) D (2)

(ii) A (1) B (2) C (4) D (3)

(iii) A (4) B (3) C (1) D (2)

(iv) A (4) B (1) C (2) D (3)

Question 60. Match the formulas of oxides given in Column I with the type of oxide given in Column II and mark the correct option.

Code :

(i) A (1) B (2) C (3) D (4)

(ii) A (4) B (1) C (2) D (3)

(iii) A (3) B (2) C (4) D (1)

(iv) A (4) B (3) C (1) D (2)

Question 61. Match the items of Columns I and II and mark the correct option.

Code :

(i) A (4) B (3) C (1) D (2)

(ii) A (3) B (4) C (1) D (2)

(iii) A (4) B (1) C (2) D (3)

(iv) A (2) B (1) C (3) D (4)

Question 62. Match the species given in Column I with the shape given in Column II and mark the correct option.

Code :

(i) A (3) B (2) C (1) D (4)

(ii) A (3) B (4) C (2) D (1)

(iii) A (1) B (2) C (3) D (4)

(iv) A (1) B (4) C (3) D (2)

Question 63. Match the items of Columns I and II and mark the correct option.

Code :

(i) A (1) B (4) C (2) D (3)

(ii) A (1) B (2) C (3) D (4)

(iii) A (2) B (1) C (4) D (3)

(iv) A (1) B (3) C (2) D (4)

Question 64. Assertion : $N_2$ is less reactive than $P_4$.

Reason : Nitrogen has more electron gain enthalpy than phosphorus.

Question 65. Assertion : $HNO_3$ makes iron passive.

Reason : $HNO_3$ forms a protective layer of ferric nitrate on the surface of iron.

Question 66. Assertion : HI cannot be prepared by the reaction of KI with concentrated $H_2SO_4$.

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

Question 67. Assertion : Both rhombic and monoclinic sulphur exist as $S_8$ but oxygen exists as $O_2$.

Reason : Oxygen forms $p\pi – p\pi$ multiple bond due to small size and small bond length but $p\pi – p\pi$ bonding is not possible in sulphur.

Question 68. Assertion : NaCl reacts with concentrated $H_2SO_4$ to give colourless fumes with pungent smell. But on adding $MnO_2$ the fumes become greenish yellow.

Reason : $MnO_2$ oxidises HCl to chlorine gas which is greenish yellow.

Question 69. Assertion : $SF_6$ cannot be hydrolysed but $SF_4$ can be.

Reason : Six F atoms in $SF_6$ prevent the attack of $H_2O$ on sulphur atom of $SF_6$.

Question 70. 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 $KMnO_4$ solution and reduces $Fe^{3+}$ to $Fe^{2+}$. Identify the solid “A” and the gas “B” and write the reactions involved.

Question 71. 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’.

Question 72. On heating compound (A) gives a gas (B) which is a constituent of air. This gas when treated with 3 mol of hydrogen ($H_2$) 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.