Question

Incorrect about alkyl halides is/ are:

• A. tertiary alkyl halides undergo $S_{N}2$ substitutions
• B. alkyl iodides on exposure to sunlight gradually darken
• C. alkyl chlorides do not give Beilstein test
• D. a nucleophilic substitution is most difficult in alkyl iodides

Answer 1

Answer: (A), (C), (D)

The correct options are
A tertiary alkyl halides undergo $S_{N}2$ substitutions
C alkyl chlorides do not give Beilstein test
D a nucleophilic substitution is most difficult in alkyl iodides

Tertiary alkyl halides undergo $S_{N}1$ substitutions as the tertiary carbocation is most stable. Hence, option A is incorrect.
Alkyl iodides on exposure to sunlight gradually darken to violet or brown color due to their decomposition to give iodine. Hence, option B is correct.
Alkyl chlorides give Beilstein test. Alkyl fluorides do not give Beilstein test. Hence, option C is incorrect.
A nucleophilic substitution is easiest in alkyl iodides. The order of reactivities is $R-I>R-Br>R-Cl>R-F$.
Hence, option D is incorrect.