Answer:
To determine the number of constitutional isomers of C4H9Br, we can generate different structures by rearranging the atoms. The molecular formula C4H9Br implies a carbon chain with four carbon atoms, and one bromine atom.
Here are the constitutional isomers for C4H9Br:
1. **n-Butyl Bromide**: This is the straight-chain isomer where the bromine atom is attached to the end carbon atom.
2. **Isobutyl Bromide**: This is an isomer with a branched chain. The bromine atom is attached to one of the middle carbon atoms in the chain.
3. **sec-Butyl Bromide**: Another branched isomer where the bromine atom is attached to one of the middle carbon atoms but in a different position compared to isobutyl bromide.
4. **tert-Butyl Bromide**: This isomer has a highly branched structure where the bromine atom is attached to a carbon atom that is part of a tertiary (3°) carbon center.
So, there are four constitutional isomers of C4H9Br. Therefore, the correct answer is (c) Four.