Answer
See the answer below.
Work Step by Step
a) Through oxidation to nitric acid and reaction with ammonia itself.
$NH_3+7/2\ O_2\rightarrow \ NO_2+3/2\ H_2O$
$NO_2+1/2\ H_2O\rightarrow 1/2\ HNO_3+1/2\ HNO_2$
$1/2\ HNO_3+1/2\ NH_3\rightarrow 1/2\ NH_4NO_3$
b) Since the reaction is exothermic, the high temperature wouldn't favor the formation of urea, but since the products-side has a lower number of moles of gases, higher pressure would favor urea formation.
