The correct option is B 0.025 g
Phenolphthalein will only neutralise 50% of CaCO3.
∴ 12 Milliequivalents of CaCO3+Milliequivalents of NaOH=Milliequivalents of HCl=110×18.5=1.85
The methyl orange indicator will neutralise the rest 50% of CaCO3.
∴ 12 Milliequivalents of CaCO3=Milliequivalents of HCl=110×2.5=0.25
∴ Milliequivalents of CaCO3=0.25×2=0.50
WCaCO3MCaCO3×2×1000=0.5
∴ WCaCO3=0.5×1002×1000=0.025 g