ICSE Class 10 Answered

The reaction for burning of sulphur is, 

We know, 

 S = 32, K = 39 , N = 14, O = 16

Moles of S reacted =

0.5 mol of S needs 0.5 mol of Oxygen,

To create confusion, x cc is mentioned in the question, which has no significant use.

So we know that Sulphur burns in 0.5 mol Oxygen.

The thermal decomposition of Potassium nitrate :

2 mols of KNO₃ gives 1 mol of O₂ 
0.5 mol of O₂ will be produced by 1 mol of KNO₃

1mol of KNO₃ = 101 g

Therefore the amount of  KNO₃ required to produce oxygen is 101 g.