Identification of Gases

Carbon dioxide gas and sulphur dioxide gas can be distinguished by using 

Name a diatomic gas that turns moist litmus paper from blue to red. 

Name the gas evolved when the aluminium powder is mixed with sodium hydroxide solution. 

Name a gas which turns lime water milky and changes the colour of acidified potassium dichromate solution from orange to green. 

Name a gas which turns moist red litmus paper blue.

Name a green solid which decomposes on heating to form carbon dioxide gas.

Oxygen turns alkaline pyrogallol solution _____.