Question

which of the following molecules can form? there is only one correct answer for this question.

Explanation:

Step1: Analyze valence - electron requirements

Carbon has 4 valence electrons, oxygen has 6, and nitrogen has 5. In a stable molecule, atoms tend to satisfy the octet rule (except hydrogen which follows the duet rule).

Step2: Check Molecule A

In $O\equiv C - O$, carbon cannot form a triple - bond with one oxygen and a single - bond with another while satisfying the octet rule for all atoms. The central carbon would have more than 8 electrons.

Step3: Check Molecule B

This appears to be an amino - acid like structure. Carbon, nitrogen, and oxygen can form bonds to satisfy their valence - electron requirements. The carbon atoms have 4 bonds, nitrogen has 3 bonds and a lone pair, and oxygen has 2 bonds and 2 lone pairs.

Step4: Check Molecule C

In $H - N\equiv N - H$, nitrogen with a triple - bond and a hydrogen each would violate the octet rule for the nitrogen atoms bonded to hydrogen as they would have more than 8 electrons around them.

Step5: Check Molecule D

The long - chain hydrocarbon with a carbonyl group at the end is a valid structure. Carbon atoms have 4 bonds and oxygen has 2 bonds, satisfying the octet rule.

Step6: Check Molecule E

The structure $O - H - O$ is not a stable molecule as written. Oxygen cannot form a stable bond with hydrogen in this way to satisfy the octet rule for all atoms.

Answer:

Molecule D