Mr(NH4NO3) = 2*Ar(N) + 4*Ar(H) + 3*Ar(O) = 2*14 + 4*1 + 3*16 = 80
w(N) = (2 * Ar(N) / Mr(NH4NO3))*100% = (2 * 14 / 80)*100% = 35%
w(H) = (4 * Ar(H) / Mr(NH4NO3))*100% = (4 * 1 / 80)*100% = 5%
w(O) = (3 * Ar(O) / Mr(NH4NO3))*100% = (3 * 16 / 80)*100% = 60%
Ответ: w(N) = 35%, w(H) = 5%, w(O) = 60%