The correct option is B Environment friendly
∙ Nitrogen dioxide is a brown coloured gas and has an irritating odour.
∙ It is used as a component in manufacturing rocket fuels too.
∙ The levels of nitrogen dioxide gas increase due to the emission from vehicles and power plants. Excess nitrogen dioxide in the atmosphere combine with rain drops to form nitric acid, which is a major contributor of acid rain. Hence, nitrogen dioxide is not an environment friendly gas.