Progestasert acts by:

The correct answer is Option (3) → Making the uterus unsuitable for implantation

Note: The given answer is as per the official NTA Answer Key. However, the question can have more than one correct answer, i.e. both Option (3) and Option (4), because NCERT says that hormone releasing IUDs make the uterus unsuitable for implantation in addition to increasing phagocytosis of sperms, which all IUDs do, as explained below.

Intra uterine devices (IUDs) are placed in the uterus to prevent pregnancy. They are of three kinds: non-medicated IUDs (Lippes loop), copper releasing IUDs (CuT, Cu7, Multiload 375) and hormone releasing IUDs (Progestasert, LNG-20). Progestasert is a hormone releasing IUD.

(1) Inhibiting the fertilising capacity of sperm — Incorrect. This is done by the copper ions released from copper releasing IUDs. Progestasert releases a hormone, not copper.

(2) Inhibiting the sperm motility — Incorrect. This too is an action of the copper ions of copper releasing IUDs.

(3) Making the uterus unsuitable for implantation — Correct. This is the special action of hormone releasing IUDs. They also make the cervix hostile to sperms. This is the answer given by NTA.

(4) Increasing phagocytosis of sperms — Also correct as per NCERT. All IUDs increase the phagocytosis (engulfing) of sperms inside the uterus. NCERT says the hormone releasing IUDs make the uterus unsuitable for implantation “in addition” to this, so Progestasert does both.

NCERT Extract:
Population Stabilisation and Birth Control – “… IUDs increase phagocytosis of sperms within the uterus and the Cu ions released suppress sperm motility and the fertilising capacity of sperms. The hormone releasing IUDs, in addition, make the uterus unsuitable for implantation and the cervix hostile to the sperms.”