ALTSM 22-2 Q-75

You can get the answer by simply substituting H with Cl and find its IUPAC nomenclature.If the name is same by any substitution then its corresponding to same compound.

In 3 we will get only 1 monochlorinated product because if you will substitute 1 H with Cl in any of methyl group,it will result in the formation of same compound.
Whereas in 1 and 2 -there can be 2 types of monochlorinated products and in 4 there can be 3 types of monochlorinated products.