A solution of ammonia and water contains 2.60*1025 water molecules and 6.90*1024 ammonia molecules. how many total hydrogen atoms are in this solution

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.