Why the lungs replaces the skin in Mammals as respiratory organ.

Name the respiratory organs of insects.

Roasting of sulphides gives the gas X as a by product. This is a colourless gas with choking smell of burnt sulphur and causes great damage to respiratory organs as a result of acid rain. Its aqueous solution is acidic, acts as a reducing agent and its acid has never been isolated. The gas X is

Skin is an accessory organ or respiration in