Which one is a chemical change: Rusting of iron or melting of iron?

Define a chemical equation. What is an unbalanced chemical equation called?

Grapes hanging on the plant do not ferment,but after being plucked from the plant,they can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

Explain,giving chemical equations,any two uses of chemical decomposition reactions in industry.

What happens when hydrogen gas is passed over heated copper oxide $(CuO)$?

State whether the following statement is true or false:
Keeping food in airtight containers helps to slow down oxidation.