Which of the following causes AIDS?

The correct answer is Option (1) → Retrovirus

AIDS means Acquired Immuno Deficiency Syndrome: a group of symptoms caused by a weak immune system, acquired during life. It is caused by HIV (Human Immuno deficiency Virus). HIV belongs to the retroviruses, which have an RNA genome inside an envelope. Inside the body, the viral RNA is copied into DNA by the enzyme reverse transcriptase, and the virus then destroys helper T-lymphocytes.

Option (1) Retrovirus — Correct. HIV is a retrovirus. By killing helper T-lymphocytes, it weakens the immune system, and this leads to AIDS.

Option (2) Influenza virus — Incorrect. The influenza virus causes flu, an infection of the respiratory tract. It does not destroy the immune system in the way HIV does.

Option (3) Plasmodium — Incorrect. Plasmodium is a protozoan. It causes malaria and is spread by the bite of the female Anopheles mosquito.

Option (4) Tuberculosis bacterium — Incorrect. The tuberculosis bacterium causes tuberculosis. TB is common in people with AIDS because their immunity is low, but it is not the cause of AIDS.

NCERT Extract:
AIDS – “The word AIDS stands for Acquired Immuno Deficiency Syndrome. This means deficiency of immune system, acquired during the lifetime of an individual indicating that it is not a congenital disease. … AIDS is caused by the Human Immuno deficiency Virus (HIV), a member of a group of viruses called retrovirus, which have an envelope enclosing the RNA genome (Figure 7.6).”