All the substances listed below are fertilizers that contribute nitrogen to the soil.
Which of these is the richest source of nitrogen on a mass percentage basis?
(a) Urea, (NH2)2 CO
(b) Ammonium nitrate, NH4 NO3
(c) Nitric oxide, NO
(d) Ammonia, NH3

Ammonia is the richest source of nitrogen on a mass percentage basis because it has 82.35% of nitrogen by mass.

Explanation:

Percentage of element in compound :

(a) Urea,

Molar mass of urea = 60 g/mol

Atomic mass of nitrogen = 14 g/mol

Number of nitrogen atoms = 2

(b) Ammonium nitrate,

Molar mass of ammonium nitrate = 80 g/mol

Atomic mass of nitrogen = 14 g/mol

Number of nitrogen atoms = 2

(c) Nitric oxide, NO

Molar mass of nitric oxide  = 30 g/mol

Atomic mass of nitrogen = 14 g/mol

Number of nitrogen atoms = 1

(d) Ammonia,

Molar mass of ammona = 17 g/mol

Atomic mass of nitrogen = 14 g/mol

Number of nitrogen atoms = 1

Ammonia is the richest source of nitrogen on a mass percentage basis because it has 82.35% of nitrogen by mass.

the answer is either b or c