13.4 g of a sample of unstable hydrated salt Na2SO4. XH2O was found to contain 6.3 g of H2O. The number of  molecules of water of crystallisation is

Weight of salt = 13.4gWeight of H2O = 6.3gWeight of anhydrous salt = 13.4 - 6.3 = 7.1gMoles of anhydrous salt = 7.1842=0.05Moles of H2O = 6.318=0.35 mol0.05 mol of anhydrous salt ⇒0.35 mol of H2O1 mole of anhydrous salt ⇒0.350.05=7 mol