How to solve Q27

According to  given  ratio of mixture of XH₄and X₂H₆ are 2:1
So the molar mass of the mixture will be 

                          =2(a+4) + (2a+6)=4a + 14

This confirms that when the mixture 4a mass of X then it have 14 g of hydrogen. 

 

Now, as it is given 5.625 g of total mixture out of which 5 g is X. 

So, the amount of hydrogen in the mixture containing 5g of X = 0.625 g 
0.625 g of hydrogen in present in 5g of X 

1g of hydrogen present in 

                                            =5/0.625 =8g
14 g of hydrogen contains                 

                                           =8×14=112 g

This 112 g of X is equivalent to 4a of X

So, molar mass of X or a = 112/4 = 28g

 

Hence the molar mass of X = 28 g and the correct option is (a)