`13.4 g` of a sample of unstable hydrated salt `Na_(2)SO_(4).XH_(2)O` was found to contains `6.3 g` of `H_(2) O`. The number of molecular of water of crystalistion is

Options

A. 5
B. 7
C. 2
D. 10

Answer

B

Explanation

Weight of salt = 13.4 g, Weight of `H_(2)O = 6.3 g`
Weight of anhydrous salt = 13.4 – 6.3 = 7.1 g
Moles of anhydrous salt `= (7.1)/(142) = 0.05` , Moles of `H_(2)O = (6.3)/(18) = 0.35` mol
0.05mol of anhydrous `rArr` salt 0.35 mol of `H_(2)O` , For 1 mole `rArr` 7 mole `H_(2)O`