Infertility in humans is due to:

The correct answer is Option (4) → Congenital diseases and immunological reasons

Infertility means being unable to conceive or produce children even after unprotected sexual co-habitation. It has many causes, which may lie in either partner.

(1) Protected sexual co-habitation — Incorrect. Protected co-habitation means contraceptives are used, so pregnancy is prevented on purpose. That is not infertility. Infertility is failure to conceive even when no protection is used.

(2) Always due to abnormalities in the female partner — Incorrect. The female is often blamed in India, but more often the problem lies in the male partner.

(3) Always due to defects in the male partner — Incorrect. The word “always” makes it wrong. The fault may be in either partner.

(4) Congenital diseases and immunological reasons — Correct. The causes are physical, congenital (present from birth), diseases, drugs, immunological or even psychological.

NCERT Extract:
Infertility – “A discussion on reproductive health is incomplete without a mention of infertility. A large number of couples all over the world including India are infertile, i.e., they are unable to produce children inspite of unprotected sexual co-habitation. The reasons for this could be many–physical, congenital, diseases, drugs, immunological or even psychological.”