Which gas is the lightest in weight?

Name the type of reaction for the following:
$(i)$ Vegetable matter changing into compost.
$(ii)$ Burning of natural gas.

What is the ratio of dihydrogen gas to dinitrogen gas used in the production of ammonia gas by Haber's process?

$A$ magnesium ribbon is burnt in oxygen to give a white compound $X$ accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen,it continues to burn and forms a compound $Y.$
$(a)$ Write the chemical formulae of $X$ and $Y.$
$(b)$ Write a balanced chemical equation,when $X$ is dissolved in water.

When air is blown from the mouth into a test-tube containing lime water,the lime water turns milky due to the presence of:

Who discovered the method for the industrial production of ammonia?