To determine the correct ordering of compounds according to the decreasing oxidation state of nitrogen, we need to calculate the oxidation number of nitrogen in each compound. The oxidation state is the hypothetical charge an atom would have if all bonds were ionic.

Step 1: Recall the rules for oxidation numbers:

• Oxidation number of hydrogen is +1 (except in metal hydrides).
• Oxidation number of oxygen is -2 (except in peroxides or with fluorine).
• The sum of oxidation numbers in a neutral compound is 0.
• The sum of oxidation numbers in an ion equals the charge of the ion.

Step 2: Calculate oxidation number of nitrogen in each compound:

HNO₃ (Nitric acid): Let oxidation state of N be x. Hydrogen is +1, oxygen is -2. The compound is neutral, so:
$\left(1\right)+x+3\times (-2)=0$
$1+x-6=0$
$x-5=0$
$x=+5$

NO (Nitric oxide): Let oxidation state of N be x. Oxygen is -2. Neutral compound:
$x+(-2)=0$
$x=+2$

NH₄Cl (Ammonium chloride): NH₄⁺ ion has charge +1. Let oxidation state of N be x. Hydrogen is +1.
$x+4\times \left(1\right)=+1$
$x+4=1$
$x=-3$

N₂ (Nitrogen gas): Elemental form, so oxidation state is 0.

Step 3: List the oxidation states:

• HNO₃: +5
• NO: +2
• NH₄Cl: -3
• N₂: 0

Step 4: Arrange in decreasing order: +5 (HNO₃) > +2 (NO) > 0 (N₂) > -3 (NH₄Cl)

So the correct order is: HNO₃, NO, N₂, NH₄Cl

Final Answer: The second option: HNO₃, NO, N₂, NH₄Cl

Related Topics and Formulae

Oxidation Number Calculation: The oxidation number is calculated using standard rules: O is -2, H is +1 (except in hydrides), and the sum equals the charge. For nitrogen, it can vary from -3 to +5.

Key Formula: For a compound, sum of oxidation numbers of all atoms = total charge.