Raunak took $5 \, mol$ of carbon atoms in a container and Krish also took $5 \, mol$ of sodium atoms in another container of the same weight. $(a)$ Whose container is heavier? $(b)$ Whose container has a greater number of atoms?

(A) The mass of sodium atoms taken by Krish $= (5 \times 23) \, g = 115 \, g$.
The mass of carbon atoms taken by Raunak $= (5 \times 12) \, g = 60 \, g$.
Since $115 \, g > 60 \, g$,Krish's container is heavier.
$(b)$ Both containers have the same number of atoms because they contain the same number of moles of atoms ($5 \, mol$ each). The number of atoms is calculated as $n \times N_A$,where $n$ is the number of moles and $N_A$ is Avogadro's constant $(6.022 \times 10^{23} \, mol^{-1})$.