Reproductive Health

Contraceptive methods and their modes of action are explained in NCERT Class 12, Chapter 4 (Reproductive Health). Copper-releasing intrauterine devices like the CuT slowly liberate copper ions into the uterine cavity, and these ions suppress sperm motility and reduce the fertilizing capacity of sperm, while also provoking a mild local reaction that hinders implantation. Permanently blocking the fallopian tubes is incorrect because that describes tubal ligation, a surgical sterilization method, not the action of an IUD. Suppressing pituitary gonadotropin release is wrong because that is the mechanism of hormonal oral pills, which prevent ovulation rather than acting locally in the uterus. Thickening cervical mucus by adding oestrogen is also incorrect, since copper IUDs are non-hormonal and do not release oestrogen, though hormone-releasing IUDs work differently. A reasoning check confirms the answer: a copper-based device placed in the uterus must act chemically through copper ions, which impair sperm and prevent fertilization, matching the question.