50 g of ${\mathrm{CaCO}}_3$ contains :

The correct option is B

0.5 moles of $\mathrm{Ca}$ atoms

The explanation for the correct option :

(B)1 mole of ${\mathrm{CaCO}}_3$= Molecular mass of ${\mathrm{CaCO}}_3$

The molecular mass of ${\mathrm{CaCO}}_3$= (Mass of $\mathrm{Ca}$$+$mass of $\mathrm{C}+3\times$Mass of $\mathrm{O}$).

= $(40+12+3\times 16)$

= 100g.

Also 1 mole of ${\mathrm{CaCO}}_3$= 1 mole of $\mathrm{Ca}$ atoms.

So, 0.5 moles of ${\mathrm{CaCO}}_3$= 0.5 mole of $\mathrm{Ca}$ atoms.

1 mole of ${\mathrm{CaCO}}_3$= 100g.

0.5 moles of ${\mathrm{CaCO}}_3$= 50g.

Explanation for the incorrect option :

(A) 50 moles of ${\mathrm{CaCO}}_3$ will be = $50\times$Molecular mass of ${\mathrm{CaCO}}_3$.

(C) 1 mole of ${\mathrm{CaCO}}_3$ = 1 mole of Calcium carbonate ions.

50g of ${\mathrm{CaCO}}_3$= 0.5 moles of Calcium carbonate ions.

(D) 1 mole of ${\mathrm{CaCO}}_3$ = 1 mole of carbon = 12g of$\mathrm{C}$ .

50g of ${\mathrm{CaCO}}_3$=0.5 moles of ${\mathrm{CaCO}}_3$= 6g of$\mathrm{C}$.

Thus, option B i.e. 50 g of ${\mathrm{CaCO}}_3$ contains 0.5 moles of $\mathrm{Ca}$ atoms is correct.