Class 12 Chemistry MCQ – P-Block Elements – Ozone

This set of Class 12 Chemistry Chapter 7 Multiple Choice Questions & Answers (MCQs) focuses on “P-Block Elements – Ozone”.

1. What is the chemical formula structure of ozone?
a) O = O+ – O
b) O – O = O+
c) O = O – O+
d) O = O+ – O
View Answer

Answer: a
Explanation: According to the Lewis dot-structure, the central oxygen atom shares a total of three electrons as a consequence of which it bears a positive charge. The oxygen to the right forms tends to attract a shared pair of electrons towards itself, thereby developing the negative charge.

2. “Ozone is a pollutant.” True or false?
a) True
b) False
View Answer

Answer: a
Explanation: Although ozone protects us from harmful UV rays, at ground level it is a highly toxic and irritating gas. It is referred to as a ‘secondary pollutant’ since it is formed from the combination of two primary pollutants, namely nitrogen oxides (NOX) and volatile organic compounds (VOCs).

3. Which of the following methods is used to form ozone from oxygen?
a) Standard electric discharge
b) Silent electric discharge
c) Thermal decomposition
d) Heating in an atmosphere of excess oxygen
View Answer

Answer: b
Explanation: Standard electric discharge produces sparking when electricity is passed through the tube. However, silent electric discharge is more appropriate because the conversion of ozone to oxygen is endothermic. The yield may be reduced by the heat from sparks.

4. As ozone transitions from solid to liquid to gas, what is the notable color change?
a) Pale blue to violet to deep blue
b) Violet to pale blue to deep blue
c) Deep blue to violet to pale blue
d) Violet to deep blue to pale blue
View Answer

Answer: d
Explanation: Ozone freezes at -192.2°C. When in solid state, it forms a violet-black structure. After melting, the color transitions to deep blue. Finally, as it is everywhere seen in the sky, ozone gas is pale blue.

5. Why is ozone a powerful bleaching agent?
a) It is highly electronegative
b) Nascent oxygen
c) Instability of molecule
d) Large negative Gibbs energy
View Answer

Answer: b
Explanation: Due to its ease in liberating nascent oxygen i.e. [O], ozone is a powerful oxidizing agent. Although, it is highly thermodynamically unstable and explosive due to large negative Gibbs energy, the ability of liberating nascent oxygen, it is considered to be one of most powerful bleaching agents.
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