Calculate the number of molecules in $0.5$ mole of water.

Which has more number of atoms?
$(i)$ $100 \, g$ of $N_2$
$(ii)$ $100 \, g$ of $NH_3$

Cinnabar $(HgS)$ is a prominent ore of mercury. How many grams of mercury are present in $225 \,g$ of pure $HgS$ (in $,g$)? Molar mass of $Hg$ and $S$ are $200.6 \,g \,mol^{-1}$ and $32 \,g \,mol^{-1}$ respectively.

Which of the following species have $18$ electrons? $Ca^{2+}, K^{+}, Na, Cl^{-}, Ar$. Also,state the reason why the chemical properties of all isotopes of an element are similar.

Calculate the number of atoms in:
$(i)$ $0.02$ moles of carbon
$(ii)$ $30$ grams of carbon
$(iii)$ $6$ moles of aluminium ions.

$3.42 \, g$ of sucrose are dissolved in $18 \, g$ of water in a beaker. The number of oxygen atoms in the solution are