moles of HCl=150*0.10*10^-3 =0.015 moles

Now according to the stoichoimetric equation:

2HCl+CaCO₃ ---> CaCl ₂ + H₂O +CO₂

 from the eqaution:

1CaCO3 mole   2mole HCl

.: Mole of CaCO3 reacted =0.015/2 moles =0.015/2 *100 gms =0.75 gms

.:% purity =0.75/1 *100 =75%

thnx.