The correct option is
C 3By giving R/S configuration to the given structures, one can find the identical compounds and the enantiomers.
R/S configuration is given by following the CIP rule.
1. If the rotation is clockwise from priority order 1 to 3 when least priority group is vertical, then it is R-configuration.
2. If the rotation is anti-clockwise from priority order 1 to 3 when least priority group is vertical, then it is S-configuration.
3. If the rotation is clockwise from priority order 3 to 1 when least priority group is horizontal, then it is R-configuration.
4. If the rotation is anti-clockwise from priority order 3 to 1 when least priority group is horizontal, then it is S-configuration.
![](https://df0b18phdhzpx.cloudfront.net/ckeditor_assets/pictures/1274667/original_7f.png)
Thus, structure (1), (2) and (4) are identical. Hence, (3) is different from the others. It is the enantiomer of other structures.