The correct answer is (c) Nitrogen.
Nitrogen is used in modern shock absorbers because it is a non-flammable gas that is also relatively inert. This means that it will not react with other chemicals in the shock absorber, and it will not catch fire or explode. Nitrogen is also a relatively dense gas, which means that it can absorb a lot of energy. This makes it ideal for use in shock absorbers, which need to be able to absorb a lot of energy from bumps in the road.
Oxygen is a flammable gas, so it is not suitable for use in shock absorbers. Hydrogen is also a flammable gas, and it is also lighter than nitrogen. This means that it would not be as effective at absorbing energy. Carbon dioxide is a heavier gas than nitrogen, but it is also a more reactive gas. This means that it is more likely to react with other chemicals in the shock absorber, and it is also more likely to catch fire or explode.
In conclusion, nitrogen is the best gas to use in shock absorbers because it is non-flammable, inert, dense, and effective at absorbing energy.