A colourless gas `X` forms a brown coloured gas when mixed with air. The gas `X` is

A colourless gas X is produced when egg shell is treated with a solution Y. The gas X turns lime water milky. What are X and Y?

When a green solid P was heated it turned into a black solid Q and a colourless gas X was released. On passing gas X, over heated carbon and another colourless gas Y was formed. Gas Y burned in oxygen to reform gas X. Name gases X and Y.

When a green solid P was heated it turned into a black solid Q and a colourless gas X was released. On passing gas X, over heated carbon and another colourless gas Y was formed. Gas Y burned in oxygen to reform gas X. What will be be observed if gas X is bubbled into lime water ?

When a green solid P was heated it turned into a black solid Q and a colourless gas X was released. On passing gas X, over heated carbon and another colourless gas Y was formed. Gas Y burned in oxygen to reform gas X. Identify P and Q.