Action of contraceptive is

The correct option is "Prevention of ovulation and fertilization only".

Understanding Contraception:
Contraceptives are devices, drugs, or methods used to prevent pregnancy. They work by interfering with the normal processes of reproduction at various stages.

Mechanism of Action of Contraceptives:
1. Prevention of Ovulation: Many hormonal contraceptives (such as oral contraceptive pills, patches, and vaginal rings) release synthetic hormones (like estrogen and progesterone) that inhibit the release of Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus. This prevents the secretion of Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) from the pituitary gland. Without the LH surge, ovulation (the release of an egg from the ovary) does not occur.
2. Prevention of Fertilization: Contraceptives can also prevent the union of sperm and egg (fertilization). Barrier methods (like condoms and diaphragms) physically block sperm from entering the uterus. Hormonal contraceptives thicken the cervical mucus, making it highly viscous and difficult for sperm to penetrate and travel up the female reproductive tract to meet the egg. Spermicides chemically disable sperm, further preventing fertilization.

Why the other options are incorrect:
- "prevent ovulation only" is too narrow, as contraceptives also prevent fertilization through barrier methods and cervical mucus thickening.
- "prevent rapid passing of eggs in oviduct" is incorrect because contraceptives do not typically speed up or slow down egg passage in a way that serves as a primary mode of contraception.
- "prevention of ovulation, implantation and fertilization only" is incorrect because modern consensus defines pregnancy as beginning at implantation; thus, preventing implantation is often distinguished from standard contraceptive actions that primarily prevent fertilization and ovulation.