Arrange Nitrogen Compounds in Decreasing Order of Oxidation State

To determine the correct sequence of nitrogen-containing compounds arranged in decreasing order of the oxidation state of nitrogen, we calculate the oxidation state of nitrogen ($\text{N}$) in each given compound:

1. In Nitric Acid ($\text{HNO}_3$): Let $x$ be the oxidation state of $\text{N}$. The oxidation states of hydrogen ($\text{H}$) and oxygen ($\text{O}$) are $+1$ and $-2$, respectively. $1 + x + 3(-2) = 0 \implies x - 5 = 0 \implies x = +5$

2. In Nitric Oxide ($\text{NO}$): Let $y$ be the oxidation state of $\text{N}$. The oxidation state of oxygen ($\text{O}$) is $-2$. $y + (-2) = 0 \implies y = +2$

3. In Elemental Nitrogen ($\text{N}_2$): Nitrogen is present in its elemental diatomic form, so its oxidation state is $0$.

4. In Ammonium Chloride ($\text{NH}_4\text{Cl}$): $\text{NH}_4\text{Cl}$ consists of $\text{NH}_4^+$ and $\text{Cl}^-$ ions. In the ammonium ion ($\text{NH}_4^+$), let $z$ be the oxidation state of $\text{N}$. The oxidation state of hydrogen ($\text{H}$) is $+1$. $z + 4(+1) = +1 \implies z + 4 = +1 \implies z = -3$

Comparing the oxidation states of nitrogen: $+5 \, (\text{HNO}_3) > +2 \, (\text{NO}) > 0 \, (\text{N}_2) > -3 \, (\text{NH}_4\text{Cl})$

Thus, the correct decreasing order of the oxidation state of nitrogen is: $\text{HNO}_3, \text{NO}, \text{N}_2, \text{NH}_4\text{Cl}$

This corresponds to Option (B).