CDS 2016 Previous Year GK Questions with Answers

The correct answer is C, Methane. Buried organic waste rots without air in a landfill, and bacteria that work without oxygen release methane.

Food scraps, paper and garden waste make up a large share of city garbage. Once they are covered in a landfill, oxygen is soon used up and anaerobic bacteria take over, producing landfill gas that is roughly half methane and half carbon dioxide. Methane is a powerful greenhouse gas, many times stronger than carbon dioxide over a short period, and it can catch fire, which is why landfill sites such as Ghazipur in Delhi often see fires. Modern landfills capture this gas and burn it to generate electricity.

A is wrong: nitrogen is the main gas of the air and is not a major product of rotting waste.

B is wrong: hydrogen forms only briefly as an intermediate and is quickly used up by other bacteria.

D is wrong: oxygen is consumed, not released, as waste decomposes.

Exam tip: rotting without air in landfills, paddy fields and cattle digestion gives methane, the main part of biogas.

The correct answer is A, Electricity, because electricity can be metered, billed and cut off, which makes it a private good. Economists call something a public good when it has two features: it is non-rival, so one person's use does not reduce what is left for others, and non-excludable, so nobody can be kept out of the benefit. Electricity fails both tests, since the unit you consume is gone and a defaulter's supply can be disconnected. This is why the market supplies power but the state must supply public goods, whose users cannot be charged individually and who therefore become free riders. Option B is wrong because national defence protects everyone in the country at once and no citizen can be left out. Option C is wrong because a lighthouse beam serves every passing ship without being used up. Option D is wrong because a public park is open to all and one more visitor takes nothing from the rest. Exam tip: public good means non-rival plus non-excludable.