Chapter 7 Groups 16, 17 & 18 - Mock Test & Solutions | Chemca.in

Maharashtra HSC Board Pattern

Chapter 7: Groups 16, 17 & 18 Mock Test

Time: 1 Hour | Maximum Marks: 25

General Instructions:

All questions are compulsory.
Section A contains Q1 (Multiple Choice) and Q2 (Very Short Answer).
Section B contains Short Answer Type I questions (2 marks each). Attempt any 4.
Section C contains Short Answer Type II questions (3 marks each). Attempt any 2.
Section D contains Long Answer questions (4 marks each). Attempt any 1.

SECTION A

Q1. Select and write the most appropriate answer from the given alternatives: [4 Marks]

The general outer electronic configuration of Group 16 elements is:

(A) $ns^2 np^3$
(B) $ns^2 np^4$
(C) $ns^2 np^5$
(D) $ns^2 np^6$
Which of the following noble gases is used in filling balloons for meteorological observations?

(A) Neon
(B) Argon
(C) Helium
(D) Krypton
Which halogen does NOT exhibit a positive oxidation state?

(A) Chlorine
(B) Bromine
(C) Iodine
(D) Fluorine
The geometry of the $XeF_4$ molecule is:

(A) Tetrahedral
(B) Square planar
(C) Octahedral
(D) See-saw

Q2. Answer the following questions in one sentence: [3 Marks]

Name the first noble gas compound prepared by Neil Bartlett.
Why is $ICl$ more reactive than $I_2$?
Write the chemical formula of Oleum.

SECTION B

Attempt any FOUR of the following: [8 Marks]

State any two anomalous properties of Oxygen.
Why is Hydrogen Fluoride (HF) a liquid at room temperature while Hydrogen Chloride (HCl) is a gas?
Write the chemical equation for the manufacture of Chlorine by Deacon's process.
Write one use each of Neon and Argon.
Draw the structures of $XeF_2$ and $XeF_6$.

SECTION C

Attempt any TWO of the following: [6 Marks]

Describe the manufacture of Sulfuric acid ($H_2SO_4$) by the Contact process. (Write only the necessary chemical equations).
What are interhalogen compounds? Explain their general classification with one example for each class.
State any three reasons for the anomalous behavior of Fluorine.

SECTION D

Attempt any ONE of the following: [4 Marks]

(a) On the basis of VSEPR theory, explain the geometry and hybridization of Chlorine trifluoride ($ClF_3$). [3 Marks]
(b) Why is Oxygen a gas but Sulfur a solid at room temperature? [1 Mark]
(a) How is Sulfur dioxide ($SO_2$) prepared from (i) Sulfur and (ii) Iron pyrites? Write the chemical equations. [2 Marks]
(b) Write any two uses of Helium gas. [2 Marks]

Self-Evaluation Guide

Solutions & Marking Scheme

SECTION A [7 Marks]

Q1. Multiple Choice Answers:

1. (B) $ns^2 np^4$ [1 Mark for correct option]

2. (C) Helium [1 Mark for correct option]

3. (D) Fluorine [1 Mark for correct option]

4. (B) Square planar [1 Mark for correct option]

Q2. Very Short Answers:

1. First noble gas compound:

Xenon hexafluoroplatinate, formula: $Xe^+[PtF_6]^-$. [1 Mark]

2. Reactivity of $ICl$ vs $I_2$:

$ICl$ is an interhalogen compound; its $I-Cl$ covalent bond is weaker and more polar than the $I-I$ bond in $I_2$, making it more reactive. [1 Mark]

3. Formula of Oleum:

$H_2S_2O_7$ (Fuming sulfuric acid). [1 Mark]

SECTION B [8 Marks]

Q3. Anomalous Properties of Oxygen:

Oxygen is a diatomic gas ($O_2$) at room temperature, while other members are polyatomic solids (e.g., $S_8$). [1 Mark]
Oxygen exhibits a maximum covalency of 4 (usually 2) due to the absence of d-orbitals, whereas other elements can expand their octet to show covalency of 6. [1 Mark]
Oxygen is paramagnetic, whereas others are diamagnetic. (Any two points accepted)

Q4. HF (liquid) vs HCl (gas):

Fluorine is highly electronegative and very small in size compared to Chlorine. As a result, HF molecules form strong intermolecular hydrogen bonds, associating them into a liquid state. [1 Mark]

Chlorine has lower electronegativity and larger size, so HCl molecules are held together only by weak van der Waals forces (dipole-dipole), making it a gas at room temperature. [1 Mark]

Q5. Deacon's Process:

Chlorine is manufactured by the oxidation of hydrogen chloride gas by atmospheric oxygen in the presence of $CuCl_2$ catalyst at 723 K.

$4HCl(g) + O_2(g) \xrightarrow{CuCl_2, 723 \text{ K}} 2Cl_2(g) + 2H_2O(g)$ [2 Marks for correct balanced equation with conditions]

Q6. Uses of Neon and Argon:

Neon: Used in discharge tubes and fluorescent bulbs for advertisement display signs (Neon signs). [1 Mark]

Argon: Used to provide an inert atmosphere in high-temperature metallurgical processes (e.g., arc welding) or in filling electric bulbs. [1 Mark]

Q7. Structures of $XeF_2$ and $XeF_6$:

$XeF_2$ (Linear): Xe is $sp^3d$ hybridized with 3 lone pairs at equatorial positions and 2 F atoms at axial positions. [1 Mark]

$XeF_6$ (Distorted Octahedral): Xe is $sp^3d^3$ hybridized with 1 lone pair and 6 bond pairs. [1 Mark]

SECTION C [6 Marks]

Q8. Contact Process for $H_2SO_4$:

1. Production of $SO_2$: $S_8(s) + 8O_2(g) \rightarrow 8SO_2(g)$ [1 Mark]

2. Catalytic oxidation of $SO_2$: $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$ (Catalyst: $V_2O_5$, 720 K) [1 Mark]

3. Absorption of $SO_3$ and dilution:
$SO_3(g) + H_2SO_4(l) \rightarrow H_2S_2O_7(l)$ (Oleum)
$H_2S_2O_7(l) + H_2O(l) \rightarrow 2H_2SO_4(aq)$ [1 Mark]

Q9. Interhalogen Compounds:

Definition: Compounds formed by the reaction between two different halogens are called interhalogen compounds (General formula $XX'_n$). [1 Mark]

Classification: Depending on the number of atoms, they are classified into four types: [2 Marks for classification + examples]

$XX'$ type (Diatomic): e.g., $ClF$, $IBr$
$XX'_3$ type (Tetraatomic): e.g., $ClF_3$, $BrF_3$
$XX'_5$ type (Hexaatomic): e.g., $IF_5$, $BrF_5$
$XX'_7$ type (Octaatomic): e.g., $IF_7$

Q10. Anomalous Behavior of Fluorine:

Size & Electronegativity: It has the smallest atomic size and highest electronegativity in the periodic table. [1 Mark]
Oxidation State: It exhibits only a -1 oxidation state, whereas other halogens exhibit positive oxidation states (+1, +3, +5, +7). [1 Mark]
Absence of d-orbitals: It cannot expand its octet because it does not have vacant d-orbitals in its valence shell. [1 Mark]

SECTION D [4 Marks]

Q11. (a) Structure of $ClF_3$ [3 Marks] (b) $O_2$ vs $S_8$ [1 Mark]

(a) $ClF_3$ Geometry:

Central atom Chlorine (Cl) undergoes $sp^3d$ hybridization. [1 Mark]

It contains 3 bond pairs (with F) and 2 lone pairs of electrons. To minimize lone pair-lone pair repulsion according to VSEPR theory, the 2 lone pairs occupy equatorial positions. [1 Mark]

This results in a T-shaped geometry for the molecule. [1 Mark]

(b) $O_2$ vs $S_8$:

Oxygen forms strong $p\pi-p\pi$ multiple bonds, existing as small diatomic $O_2$ molecules held by weak van der Waals forces (Gas). Sulfur is larger, cannot form $p\pi-p\pi$ bonds, and exists as large puckered $S_8$ rings held by stronger van der Waals forces (Solid). [1 Mark]

Q12. (a) Preparation of $SO_2$ [2 Marks] (b) Uses of Helium [2 Marks]

(a) Preparation of $SO_2$:

From Sulfur: $S_8(s) + 8O_2(g) \rightarrow 8SO_2(g)$ [1 Mark]

From Iron Pyrites: $4FeS_2(s) + 11O_2(g) \rightarrow 2Fe_2O_3(s) + 8SO_2(g)$ [1 Mark]

(b) Uses of Helium:

Used in filling weather balloons and airships because it is non-combustible and light. [1 Mark]
Used as a diluent for oxygen in deep-sea diving apparatus (because of its very low solubility in blood). [1 Mark]

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