How combination reaction differs from decomposition reaction?

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.

Give differences between Oxidation and Reduction.

Differentiate between displacement and double displacement reactions.

What is observed when:

(i) Potassium iodide is added to aqueous lead nitrate?

(ii) Identify the type of reaction.

(iii) Give a balanced chemical equation for this.