CaCO₃=100 g MW

150 ml 0.1 M HCl=.015 moles HCl

CaCO₃ 1 mole reacts with 2 moles HCl

so amt of lime stone=0.015/2 moles=0.015/2*100g=0.75 grams

so 0.75 g limestone/1 g sample

percanetage purity=75