(a)
$N_{2}(g) + 3H_{2}(g) \rightleftharpoons 3NH_{3}(g) + 92.3\ kJ$
According to Le-Chatelier’s principle, the favourable conditions for the reaction are
Low temperature (as the reaction is exothermic)
High pressure (volume is decreasing)
Constant removal of ammonia gas as it is formed.