Question

How many molecules of water are there in 36g water

Answer 1

Avogadro's Number ($N_A$) = the number of molecules of a substance in one mole of a substance.
That means that in one mole of water, there are $N_A$ water molecules.
1 mole of water = 18 grams.
no. of moles = $\frac{givenmass}{molarmass}=\frac{36}{18}=2$
Hence,36 grams of water has two moles of water.
No. of molecules = No. of moles $\times Avagadrono.$
= $2\times 6.022\times {10}^{23}=12.044\times {10}^{23}$