How many constitutional isomers are produced?

Question

In regards to the mono-chlorination of 2,2-dimethylbutane

Answer 1

The substrate is (CH3)3C-CH2CH3. So you put one Cl on any of the first CH3's, and that's one isomer. Put one on the CH, and that's the second isomer. Finally, put a Cl on the end CH3, and that's the third isomer.