The incorrect resonance structure of diazomethane is (a) \(\mathrm{H}_{2} \stackrel{\ominus}{\cdots}-\mathrm{N} \equiv \cdots\) (b) \(\mathrm{CH}_{3}-\mathrm{N}=\cdots \mathrm{N}\) (c) \(\mathrm{H}_{2} \mathrm{C}=\stackrel{\oplus}{\mathrm{N}}=\cdots \mathrm{N}^{\cdot}\) (d) \(\mathrm{H}_{2} \mathrm{C} \rightarrow \ddot{\mathrm{N}}=\cdots^{\ominus}\)

Diazomethane is a compound with the formula CH2N2. The central carbon atom is single-bonded to two hydrogen atoms and double-bonded to one nitrogen atom, and the nitrogen atoms are connected to each other with a double bond.

The octet rule states that atoms will gain, lose, or share electrons in order to have eight valence electrons. Now, we need to apply the octet rule to each resonance structure and check if it is followed. (a) \(\mathrm{H}_{2} \stackrel{\ominus}{\cdots}-\mathrm{N} \equiv \cdots\) In this structure, nitrogen to the left has more than eight valence electrons, which violates the octet rule. Hence, this structure is incorrect. (b) \(\mathrm{CH}_{3}-\mathrm{N}=\cdots \mathrm{N}\) In this structure, all atoms follow the octet rule. (c) $\mathrm{H}_{2} \mathrm{C}=\stackrel{\oplus}{\mathrm{N}}=\cdots \mathrm{N}^{\cdot}$ In this structure, all atoms follow the octet rule. (d) \(\mathrm{H}_{2} \mathrm{C} \rightarrow \ddot{\mathrm{N}}=\cdots^{\ominus}\) In this structure, all atoms follow the octet rule.

Based on our analysis, the first resonance structure (a) is the incorrect one, as the nitrogen atom to the left has more than eight valence electrons, violating the octet rule. So, the answer is (a) \(\mathrm{H}_{2} \stackrel{\ominus}{\cdots}-\mathrm{N} \equiv \cdots\).