(a)
We know that protons in 1 mole $CaCO_{3}$
=atomic number of calcium + atomic number of carbon + 3 (atomic number of oxygen)
$= 20 + 6 + 3(8) = 50$ mol
$\therefore Proton\ in\ 10\ g\ CaCO_{3} = \frac{10 \times 50}{100} \times 6.02 \times 10^{23}$
$= 3.01 \times 10^{24}$