Which gas is responsible for acid rain?

$NH_{3}$ is used in the preparation of nitric acid by $.....$ process.

$(a)$ Balance the chemical equation:
$Fe(s) + H_2O(g) \rightarrow Fe_3O_4(s) + H_2(g)$
$(b)$ Identify the type of reaction in the equation given below:
$Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) + NaCl(aq)$

In the presence of which catalyst is sulphur dioxide heated at high temperature to form sulphur trioxide?

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?

Name the type of reaction for the following:
$(i)$ Vegetable matter changing into compost.
$(ii)$ Burning of natural gas.