Practice MCQ Questions and answers on Chemistry-GK

1

Bleaching action of moist sulphur dioxide is because of its

A) Basic property B) Acidic property C) Oxidising property D) Reducing property

Discuss

Answer & Solution

Answer: Option C

Solution:

In moist conditions, sulphur dioxide is a bleaching agent. In the reducing action of SO₂, oxygen is removed from coloured dye. Sulphur dioxide is used to bleach wool and silk. Salts of sulphur dioxide are also used in bleaching. Calcium hydrogen sulphite Ca(HSO₃)₂ is used to whiten wood pulp in the manufacturing of paper. Other than SO₂, sodium hydrosulphite (Na₂S₂O₄) is also used to bleach wool. However, bleaching using SO₂ is not permanent. On exposure to air and light, the original colour slowly returns as oxygen in air oxidises the bleached substance.

2

Sulphur dioxide bleaches colouring matter by :

A) Reduction B) Dehydration C) Decomposition D) Oxidation

Discuss

Answer & Solution

Answer: Option A

Solution:

Sulphur dioxide gas exhibits bleaching properties in presence of moisture. It dissolves in water liberating nascent hydrogen. Nascent hydrogen removes oxygen atoms from the colouring matter (reduces colouring matter) and it loses its colour.

3

Which one of the following is commonly used for pulp bleaching in the paper industry?

A) Mild sulphuric acid B) Glucose isomerase C) Hydrogen peroxide D) Iodine and water

Discuss

Answer & Solution

Answer: Option C

Solution:

Bleaching of wood pulp is the chemical processing carried out to decrease the color of the pulp, so that it becomes whiter.Alkaline hydrogen peroxide is the most commonly used bleaching agent for mechanical pulp. It selectively oxidizes non-aromatic conjugated groups responsible for absorbing visible light. The decomposition of hydrogen peroxide is catalyzed by transition metals.

4

In upper layer of atmosphere ozone is formed by

A) The action of ultraviolet rays on oxygen B) The combination of oxygen molecules C) Subjecting oxygen to high pressure D) The action of nitrogen on oxygen in atmosphere

Discuss

Answer & Solution

Answer: Option A

Solution:

In upper layer of atmosphere ozone is formed by the action of ultraviolet rays on oxygen.

5

Which one of the following is used to restore the colour of old oil paintings ?

A) Ozone B) Hydrogen peroxide C) Barium peroxide D) Sodium peroxide

Discuss

Answer & Solution

Answer: Option B

Solution:

Hydrogen peroxide is used to restore the colour of old oil paintings containing lead oxide.

6

Ozone consists of

A) Oxygen only B) Oxygen and Nitrogen C) Hydrogen and Carbon D) Oxygen and Carbon

Discuss

Answer & Solution

Answer: Option A

Solution:

Ozone is a gas made up of three oxygen atoms (O3). It occurs naturally in small (trace) amounts in the upper atmosphere (the stratosphere).

7

Ozone layer is present in

A) Troposphere
B) Ionosphere
C) Stratosphere
D) Exosphere

Discuss

Answer & Solution

Answer: Option C

Solution:

Most atmospheric ozone is concentrated in a layer in the stratosphere, about 9 to 18 miles (15 to 30 km) above the Earth's surface (see the figure below). Ozone is a molecule that contains three oxygen atoms. At any given time, ozone molecules are constantly formed and destroyed in the stratosphere.

8

The presence of ozone in the stratosphere is responsible for

A) Increasing the average global temperature in recent years B) Higher rate of photosynthesis
C) Checking the penetration of ultraviolet rays to the earth D) Supplying oxygen for people travelling in jets

Discuss

Answer & Solution

Answer: Option C

Solution:

Ozone in the stratosphere protects us from the Sun's harmful ultraviolet rays. However, ozone in the troposphere, closer to Earth's surface, is a pollutant and hazardous to our health.

9

The major use of sulphur is in the manufacture of

A) H₂SO₄ B) H₂S C) SO₂ D) Fungicide

Discuss

Answer & Solution

Answer: Option A

Solution:

The major use of sulphur is in the manufacture of sulphuric acid (H₂SO₄) which is one of the most important compounds made by the chemical industry. It is used to make, literally, hundreds of compounds needed by almost every industry.

10

Percentage of lead in lead pencils is

A) 0 B) 31-66 C) 40 D) 80

Discuss

Answer & Solution

Answer: Option A

Solution:

There is no percentage of lead in lead pencils, or we can say zero percentage of lead. The pencils are nowadays made of graphite, which is an allotrope of carbon.