Which one of the following infections is completely curable?

The correct answer is Option (2) → Gonorrhoea

Most sexually transmitted infections are completely curable if detected early and treated properly. NCERT names three exceptions: hepatitis-B, genital herpes and HIV.

Option (2) Gonorrhoea — Correct. Gonorrhoea is a sexually transmitted infection that is not one of the three exceptions, so it can be completely cured.

NCERT Extract:
Sexually Transmitted Infections (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. Except for hepatitis-B, genital herpes and HIV infections, other diseases are completely curable if detected early and treated properly.”
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.”