You must first calculate the total weight of 1 mole of the substance. You do this by finding the molar weights on the periodic table of each of the elements in the compound:

So now we take the amount of each element that is given in the compound and divide it by the total mass of the compound:
Carbon: 96.08g

Carbon = 49.48%
Nitrogen: 56.028g

Nitrogen = 28.85%
Oxygen: 31.998g

Oxygen = 16.48%
Answer is: mass of 1,58 mol of water is 28,44 grams.
n(H₂O) = 1,58 mol.
M(H₂O) = 2 · 2 g/mol + 16 g/mol.
M(H₂O) = 18 g/mol.
m(H₂O) = n(H₂O) · M(H₂O).
m(H₂O) = 1,58 mol · 18 g/mol.
m(H₂O) = 28,44 g.
n - amount of substance.
M - molar mass.
Electrical energy or the answer C