Chemistry (Part-3) (CDS-Solved Paper)

Total Questions: 18

1. In tritium (T) , the number of protons (p) and neutrons (n) respectively are [Evening Shift-2014 (II)]

Correct Answer: (b) 1 and 2
Solution:

Tritium is very heavy hydrogen isotope of mass number 3. It is represented as ₁³H. . In tritium, number of protons (p) is 1 and number of neutrons (n) are (3 - 1 = 2).

2. When carbon dioxide is passed through lime water, the solution turns milky, but on prolonged passage, the solution turns clear. This is because [Evening Shift-2014 (II)]

Correct Answer: (a) the calcium carbonate formed initially is converted to soluble calcium bicarbonate on passage of more carbon dioxide
Solution:

When carbon dioxide (CO₂) is passed through lime water, the lime water turns milky due to the formation of a white precipitate of calcium carbonate.
If excess of CO2 is passed through lime water, then the white precipitate formedfirst dissolves due to the formation of calcium bicarbonate and the solution becomes clear again.

3. The form of carbon known as graphite [Evening Shift-2014 (II)]

Correct Answer: (c) is a better electrical conductor than diamond
Solution:

The two common allotropes of carbon are diamond and graphite. Graphite is a good conductor of electricity whereas diamond is a non-conductor of electricity.
In a graphite crystal, each carbon atom is joined to only three other carbon atoms by covalent bonds. The fourth valence electron of each carbon atom is ‘free’ to move, which is responsible for the conduction of electricity.
Where as in a diamond crystal, each carbon atom is linked to four other carbon atoms by strong covalent bonds.

4. Which one among the following is an example of chemical change? [Evening Shift-2014 (II)]

Correct Answer: (c) The frying of an egg
Solution:

The change which affects the composition as well as chemical properties of matter and result in the formation of a new substance is called a chemical change. Chemical changes are generally irreversible. So, the frying of an egg is a chemical change.

5. Which of the following is not correct about baking soda? [Evening Shift-2014 (II)]

Correct Answer: (c) It is a corrosive base
Solution:

Baking soda (NaHCO₃)is a mild, non-corrosive base. It is used as an antacid in medicine to remove acidity of the stomach. It is also used for faster cooking and in soda acid fire extinguisher.

6. Chromium oxide in paints makes the colour of paint [Evening Shift-2014 (II)]

Correct Answer: (a) green
Solution:

Chromium oxide, cuprous oxide and cobalt oxide in paints make the colour of paint green, red and blue respectively.

7. Carbon or graphite rods are used in atomic reactors as moderators for sustained nuclear chain reaction through nuclear fission process. In this process [Evening Shift-2014 (II)]

Correct Answer: (c) the neutrons are made slow
Solution:

The substances, such as carbon or graphite are used to slow down, fast moving neutron because of the following:
● It has low atomic weight.
● It does not absorb neutron.
● It should undergo elastic collisions with neutrons and reduce their velocity.

8. The distribution of electrons into different orbits of an atom, as suggested by Bohr, is [Evening Shift-2014 (II)]

Correct Answer: (c) 2 electrons in the K-orbit, 8 electrons in the L-orbit and 18 electrons in the M-orbit
Solution:

According to Bohr, the distribution of electrons into different orbits of an atom is given by 2n² , where, n is number of orbits.

9. Read the following statements carefully and choose the correct option. [Morning Shift-2014 (I)]

Statement I During indigestion, milk of magnesia is taken to get rid of pain in the stomach.
Statement II Milk of magnesia is a base and it neutralises the excess acid in the stomach. Codes

Correct Answer: (a) Both the statements are individually true and Statement II is the correct explanation of Statement I
Solution:

Milk of magnesia or magnesium hydroxide is an inorganic compound. During indigestion, milk of magnesia is taken to get rid of pain in the stomach. It is used as an antacid to relieve indigestion, sour stomach and heart burn.
Hence, option (a) is true.

10. Date of manufacture of food items fried in oil should be checked before buying because oils become rancid due t [Morning Shift-2014 (I)]

Correct Answer: (a) oxidation
Solution:

Oil become rancid due to oxidation. It react with food in presence of oxygen and become rancid. Rancid oil is a major source of destructive free radicals in our diet.