Which among the following determines the sex of the child?

Sex chromosomes of father.

The correct answer is Option (1)- Sex chromosomes of father.

A child's biological sex is determined by the combination of sex chromosomes inherited from the parents. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

During reproduction, the mother always contributes an X chromosome because she has only X chromosomes. The father's sperm can carry either an X or a Y chromosome.

• If the sperm carrying an X chromosome fertilizes the egg, the resulting combination is XX, which means the child will be female.
• If the sperm carrying a Y chromosome fertilizes the egg, the combination is XY, resulting in a male child.

Therefore, the sex of the child is determined by the chromosome (X or Y) that the father contributes.