AIIMS 2006 Chemistry Chemical Bonding Assertion Reason Question

To tackle this question, we need to analyze both the assertion and the reason provided.

Assertion:

Molecular nitrogen is less reactive than molecular oxygen.

This statement is true. Molecular nitrogen ($N_2$) is indeed less reactive than molecular oxygen ($O_2$). This is primarily due to the nature of the triple bond in nitrogen, which is much stronger and more stable than the double bond in oxygen. The $N \equiv N$ bond in nitrogen involves three bonds (one sigma bond and two pi bonds), which makes it very stable and resistant to breaking. In contrast, the $O = O$ bond in oxygen is weaker and more easily broken, making oxygen more reactive in chemical reactions.

Reason:

The bond length of $N_2$ is shorter than that of oxygen.

This statement is also true. The bond length in $N_2$ is approximately 1.10 Å, while the bond length in $O_2$ is around 1.21 Å. A shorter bond length typically indicates a stronger bond, which is consistent with the fact that $N_2$ has a triple bond compared to the double bond in $O_2$.

Correct Answer: A

Since both the assertion and the reason are true, and the reason provides a correct explanation for the assertion (the greater bond strength and shorter bond length of $N_2$ contribute to its lower reactivity), the correct answer is A.

Explanation of Other Options:

• B: This option states that both the assertion and reason are true, but the reason is not the correct explanation of the assertion. This is incorrect because the reason does indeed explain why nitrogen is less reactive than oxygen, due to the strength and stability conferred by the shorter bond length.

• C: This option claims that the assertion is true but the reason is false. This is incorrect as both statements are true.

• D: This option asserts that both the assertion and the reason are false. This is clearly incorrect since we have established both statements to be true.

Summary:

In conclusion, the bond characteristics of nitrogen and oxygen play a crucial role in their chemical reactivity. The strong triple bond in nitrogen leads to its lower reactivity compared to the double bond in oxygen. The bond lengths and bond strengths are essential concepts in understanding the chemical properties of these molecules, reinforcing the validity of both the assertion and the reason. Thus, the answer is A.