State the kind of chemical reactions in the following examples:
$(a)$ Digestion of food in the stomach
$(b)$ Combustion of coal in air.

Observe the given figure and answer the following questions:
$(i)$ Write the complete balanced chemical equation for the reaction.
$(ii)$ Write the type of reaction involved.
$(iii)$ Is there any precipitate formed?
$(iv)$ If any precipitate is formed,write the colour of the precipitate.

Which of the following statements about the given reaction are correct?
$3 Fe (s) + 4 H_2 O (g) \rightarrow Fe_3 O_4 (s) + 4 H_2 (g)$
$(i)$ Iron metal is getting oxidised
$(ii)$ Water is getting reduced
$(iii)$ Water is acting as reducing agent
$(iv)$ Water is acting as oxidising agent

Which of the following is not a physical change?

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

Balance the following chemical equation:
$Fe(s) + H_2O(g) \rightarrow Fe_3O_4(s) + H_2(g)$