1 molecule of NH3 has 3 atoms of H.
6.90*10²⁴ molecules NH3 have 3*6.90*10²⁴ =20.7*10²⁴ atoms H=2.07*10²⁵ atoms H
1 molecule H2O of has 2 atoms of H.
2.60*10²⁵ molecules of H2O have 2*2.60*10²⁵ =5.20 *10²⁵ atoms of H
2.07*10²⁵ + 5.20 *10²⁵ =7.27*10²⁵ atoms of H altogether.
