Answer:
2-chloro-p-dimethylbenzene
Step-by-step explanation:
The only compound that fulfills those conditions (a tribsubstituted aromatic ring where the methyl groups are oriented para) is 2-chloro-1,3-dimethylbenzene.
Once the 1 and 4 positions are taken, no matter where we put the Cl species, the end result is going to be the same molecule.
Attached below is a picture of the compound.