Which among the following is correct about the cause of transmission…

The correct answer is Option (4) → All of these

Hepatitis-B is a sexually transmitted infection (STI). Like HIV, it can also spread in other ways in which the blood of an infected person enters a healthy person. So it passes by sex, by shared needles and by blood transfusion. It is also one of the STIs that is not completely curable.

Option (1) By sexual contact. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Hepatitis-B is an STI, so it does pass by sexual contact.

Option (2) By sharing of injection needles. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Sharing injection needles with infected persons passes the virus on.

Option (3) By transfusion of blood. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Transfusion of infected blood also passes the virus on.

NCERT Extract:
Sexually Transmitted Infections (STIs) – “Infections or diseases which are transmitted through sexual intercourse are collectively called sexually transmitted infections (STI) or venereal diseases (VD) or reproductive tract infections (RTI). Gonorrhoea, syphilis, genital herpes, chlamydiasis, genital warts, trichomoniasis, hepatitis-B and of course, the most discussed infection in the recent years, HIV leading to AIDS are some of the common STIs. … Some of these infections like hepatitis–B and HIV can also be transmitted by sharing of injection needles, surgical instruments, etc., with infected persons, transfusion of blood, or from an infected mother to the foetus too.”