The number of water molecules in 3.6 g of water ($\mathrm{H}{}_2\mathrm{O}=18\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$) is (take $N_A=6.02\times 10^{23}\mathrm{mo}{\mathrm{l}}^{-1}$)

Moles of water = 3.6/18 = 0.2. Number of molecules = moles x $N_A$ = 0.2 x 6.02e23 = 1.204e+23. The other values correspond to using the mass directly, counting atoms, or counting electrons.