Identify, which is not the sexually transmitted infection?

The correct answer is Option (3) → Rheumatoid arthritis

Sexually transmitted infections (STIs) spread through sexual intercourse.

Option (1) Chlamydiasis — An STI.

Option (2) Trichomoniasis — An STI.

Option (3) Rheumatoid arthritis — Not an STI. It is an autoimmune disease, in which the body’s immune system attacks its own joints.

Option (4) Syphilis — An STI.

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.”
Auto Immunity – “… Rheumatoid arthritis which affects many people in our society is an auto-immune disease.”