List two observations which you record while burning magnesium in air.

Give reasons for the following:
$(i)$ Moist air and acidic gases are not good for some metals.
$(ii)$ Chips manufacturers usually flush bags of chips with nitrogen gas.

The substances which get oxidised easily can be kept for longer duration by:

Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.

What is rancidity? Mention any two ways by which rancidity can be prevented?

$A$ student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the chemical name of black and green coatings.