Count Elements Showing Only One Non Zero Oxidation State

To determine the number of elements showing only one non-zero oxidation state, let us analyze the possible oxidation states for each given element:

1. Oxygen ($\text{O}$): Exhibits multiple oxidation states such as $-2$ (in $\text{H}_2\text{O}$), $-1$ (in $\text{H}_2\text{O}_2$), $-\frac{1}{2}$ (in $\text{KO}_2$), $+1$ (in $\text{O}_2\text{F}_2$), and $+2$ (in $\text{OF}_2$).
2. Chlorine ($\text{Cl}$): Exhibits multiple oxidation states including $-1, +1, +3, +5,$ and $+7$.
3. Fluorine ($\text{F}$): Being the most electronegative element, it exhibits only one non-zero oxidation state, which is $-1$ (e.g., in $\text{HF}$).
4. Nitrogen ($\text{N}$): Exhibits multiple oxidation states ranging from $-3$ to $+5$ (e.g., $-3$ in $\text{NH}_3$, $+3$ in $\text{HNO}_2$, $+5$ in $\text{HNO}_3$).
5. Phosphorus ($\text{P}$): Exhibits multiple oxidation states such as $-3, +3,$ and $+5$.
6. Tin ($\text{Sn}$): Exhibits variable oxidation states of $+2$ and $+4$.
7. Thallium ($\text{Tl}$): Exhibits variable oxidation states of $+1$ and $+3$ due to the inert pair effect.
8. Sodium ($\text{Na}$): As an alkali metal, it exhibits only one non-zero oxidation state, which is $+1$ (e.g., in $\text{NaCl}$).
9. Titanium ($\text{Ti}$): Being a transition element, it exhibits multiple oxidation states such as $+2, +3,$ and $+4$.

Thus, the elements showing only one non-zero oxidation state are $\text{F}$ (oxidation state $-1$) and $\text{Na}$ (oxidation state $+1$).

Therefore, the total number of such elements is 2.