Give differences between Oxidation and Reduction.

What happens when:

(a) copper powder is heated in a china dish?

(b) hydrogen gas is passed over hot copper (II) oxide?

A student has found black coating on his silver coins and green coating on his copper coins. Which chemical phenomenon is responsible for this? Write chemical name of these coatings.

How combination reaction differs from decomposition reaction?

Differentiate between displacement and double displacement reactions.