The part of the human sperm that helps in the fertilisation of the ovum is a cap-like structure called :

Acrosome

The correct answer is Option (2)- Acrosome.

The acrosome is a cap-like structure located at the tip of the sperm's head. It contains enzymes that play a critical role in helping the sperm penetrate the protective layers of the egg (ovum) during the fertilization process. The acrosome's enzymatic action is necessary for the successful fusion of the sperm with the egg.

The other options are not directly involved in the fertilization process:

Head: While the head of the sperm contains the nucleus and the acrosome, it is the acrosome specifically that plays a role in fertilization.

Middle piece: The middle piece of the sperm contains mitochondria, which generate energy for the sperm's motility but are not directly involved in the fertilization of the ovum.

Tail: The tail, or flagellum, is responsible for the movement of the sperm and is not directly involved in the fertilization process.