Explanation:

The given molecular formula is C4H7Cl.

Step 1: Draw the possible structures

The possible structures can be drawn by considering all possible arrangements of atoms and bonds.

Step 2: Identify the isomers

After drawing all possible structures, we need to identify the isomers. Isomers are compounds with the same molecular formula but different structural arrangements.

Step 3: Count the number of isomers

Count the number of isomers obtained from the above steps.

The possible structures and their respective isomers are given below:

1. Chain isomerism

a. n-butyl chloride
b. isobutyl chloride

2. Position isomerism

a. 1-chlorobutane
b. 2-chlorobutane
c. 3-chlorobutane

3. Functional isomerism

a. 1-chlorobutene
b. 2-chlorobutene

Total number of isomers = 2 + 3 + 2 = 7

Step 4: Cross-check the answer

We can also cross-check the answer by using the formula for counting structural isomers, which is 2^n, where n is the number of carbon atoms in the molecule.

Here, n = 4 (number of carbon atoms)

Therefore, number of structural isomers = 2^4 = 16

Out of these 16 isomers, some are repeated due to symmetry and identical arrangements. After removing the duplicates, we get the final answer as 12.

Hence, the correct answer is option (C) 12.