What is the function of copper-T

The correct option is "stops fertilization".

The copper-T (Cu-T) is a widely used intrauterine device (IUD) inserted into the uterus to prevent pregnancy. Its primary mechanism of action relies on the continuous release of copper ions (Cu²⁺) into the uterine cavity.

These released copper ions have a strong spermicidal effect. They suppress sperm motility (movement) and significantly reduce the fertilizing capacity of the sperm. Because the sperm are rendered unable to reach or penetrate the ovum, fertilization is prevented from taking place.