How can duplication of a chromosome of the first pair produce a double head and at the same time affect wing pigmentation and body segment

Duplication of chromosome can cause multiple genes to work in an uncontrolled manner.

Explanation:

There are numerous genes that are encoded by the chromosome. The duplication in the chromosome can cause multiple genes to go out of control that can cause patterning of the body and head which can influence the wing patterning or pigmentation. For example in Down's syndrome the three copies of chromosome number 21 are formed which is the trisomy of chromosome number 21 which can cause developmental issues in humans symptoms are flattened face, short neck, small ears, and others.

answer; i believe that the correct answer is (light);

that is wrong, its not thymus.