Which of the following is a major component of water pollution?

The pollutants which come directly into the air from sources are called primary pollutants. Primary pollutants are sometimes converted into secondary pollutants. Which of the following belongs to secondary air pollutants?

What is the percentage of oxygen by volume in dry air (in $\%$)?

What do you mean by green chemistry? How will it help decrease environmental pollution?

The gas known as a greenhouse gas is ...... .

Identify the pollutant gases largely responsible for the discoloured and lustreless nature of marble of the Taj Mahal.