Isomerism between Alkyl Cyanides and Isocyanides:

Isomers are compounds that have the same molecular formula but different structures. Alkyl cyanides and isocyanides are isomeric compounds that have the same molecular formula, but different structures.

Explanation:

Alkyl cyanides: Alkyl cyanides have the general formula R-CN, where R is an alkyl group attached to a cyano group (C≡N). In alkyl cyanides, the cyano group is attached to the carbon atom of the alkyl group.

Isocyanides: Isocyanides have the general formula R-N≡C, where R is an alkyl group attached to an isocyanide group (N≡C). In isocyanides, the isocyanide group is attached to the nitrogen atom of the alkyl group.

Isomeric Relationship: Alkyl cyanides and isocyanides are isomeric compounds because they have the same molecular formula (CnH2n+1N) but differ in the connectivity of atoms. In alkyl cyanides, the cyano group is attached to the carbon atom, while in isocyanides, the isocyanide group is attached to the nitrogen atom.

Comparison with Other Options:

- Diazonium salts: Diazonium salts have the general formula R-N2+X-, where R is an organic group and X is an anion. They are not isomeric with alkyl cyanides.
- Nitroalkanes: Nitroalkanes have the general formula R-NO2. They are not isomeric with alkyl cyanides.
- Ethers: Ethers have the general formula R-O-R', where R and R' are alkyl or aryl groups. They are not isomeric with alkyl cyanides.

Therefore, the correct option is Isocyanides (Option D) as they are isomeric with alkyl cyanides due to their similar molecular formula but different structural arrangements.