Question

Assertion :$N{O}_2$ is reddish brown and its dimer $N_2{O}_4$ is colourless. Reason: There is a dative bond formation between two $N{O}_2$ molecules.

• A. Both assertion and reason are CORRECT and reason is the CORRECT explanation of the assertion.
• B. Both assertion and reason are CORRECT, but reason is NOT THE CORRECT explanation of the assertion.
• C. Assertion is CORRECT, but reason is INCORRECT.
• D. Assertion is INCORRECT, but reason is CORRECT.

Answer 1

The correct option is C Assertion is CORRECT, but reason is INCORRECT.

For assertion:
Le Chateliers Principle states that if a system at equilibrium is subjected to a change of conditions, reactions occur in the system that tend to counteract the imposed change.
Thus, $N{O}_2$ is an odd electron molecule that does not obey the octet rule. It readily dimerizes to form the colorless $N_2{O}_4$ molecule that does obey the octet rule. The $N{O}_2-N_2{O}_4$ equilibrium is established as soon as the $N{O}_2$ is produced and it temperature dependent.
For reason:
Oxygen has six electrons in the free atom, and it has six electrons in the right-hand oxygen. Therefore, the right-hand oxygen has no formal charge because it has the same number of electrons in the NO2 - molecule as it does as an atom. The left-hand, singly bonded oxygen has seven electrons- one more electron than has the free atom. Therefore, this oxygen has a -1 formal charge because it has one more electron in the molecule than oxygen has as a free atom. The nitrogen has five electrons around it and five valence electrons in the free atom, so the N has no formal charge. Thus, there is no dative or covalent bond formation occurs between two, $N{O}_2$ molecules.