If $10^{21}$ molecules are removed from $200 \text{ mg}$ of $CO_2$, then the number of moles of $CO_2$ remaining is .......... $\times 10^{-3}$.

$4.4 \ g$ of $CO_2$ and $2.24 \ L$ of $H_2$ at $\text{STP}$ are mixed in a container. The total number of molecules present in the container will be :

$A$ sample of $[Cu(NH_3)_4]SO_4$ contains $2.4 \times 10^{24}$ ammonia molecules. The moles of $[Cu(NH_3)_4]SO_4$ in the given sample will be:

$A$ thin layer of cobalt is deposited on a plate with a total area of $0.5 \ m^2$ and a thickness of $0.005 \ cm$. How many cobalt atoms are deposited on the plate? (Density of cobalt $= 8.9 \ g \ cm^{-3}$,Atomic mass of $Co = 59 \ g \ mol^{-1}$)

Which one of the following will have the largest number of atoms?
$(i)$ $1 \,g$ $Au_{(s)}$
$(ii)$ $1 \,g$ $Na_{(s)}$
$(iii)$ $1 \,g$ $Li_{(s)}$
$(iv)$ $1 \,g$ of $Cl_{2(g)}$

Which gas among the following contains the maximum number of molecules at $STP$? (Molar masses in $g \ mol^{-1}$: $CO_{2}=44, Ar=39.9, CH_{4}=16, O_{2}=32$)