18 g of H2O has 2N hydrogen atoms in it and H3:H1 is 9.0×10−18:1
18 g of H2O contains (9.0×10−18×6.023×1023×2)H3 atoms
10 g of H2O contains (9.0×10−18×6.023×1023×2)×1018=6.023×106 atoms of H3
t=2.303klogNoN
46=2.303×6.930.693log6.023×106N
log6.023×106N=46×0.6932.303×6.93=2
log(6.023×106)=2+logN
logN=4.78≈5