Identify the cations and anions present (if any) in the following compounds:
$(a)$ $CH_3COONa$
$(b)$ $NaCl$
$(c)$ $H_2$
$(d)$ $NH_4NO_3$

$(i)$ $(a)$ What do you understand by $1 \text{ amu}$ or $1 \text{ u}$?
$(b)$ How is it linked with relative atomic mass?
$(ii)$ How do we know the presence of atoms if they do not exist independently for most of the elements?

Verify by calculating that:
$(a)$ $5$ moles of $CO_2$ has a higher mass than $5$ moles of $H_2O$.
$(b)$ $120 \, g$ of calcium and $120 \, g$ of magnesium elements have a mole ratio of $3:5$.

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.

The chemical symbol for sodium is

What weight of sodium contains the same number of atoms as are present in $16\, g$ of sulphur (in $, g$)?