**Core Concept**
Aplastic anaemia is a rare but serious condition characterized by bone marrow failure, leading to a decrease in the production of blood cells. This condition can be caused by various medications, particularly those that interfere with DNA synthesis or cause oxidative stress.

**Why the Correct Answer is Right**
Chloramphenicol is a broad-spectrum antibiotic that inhibits protein synthesis by binding to the 50S subunit of the bacterial ribosome. However, it also has a rare but well-documented side effect of causing bone marrow suppression, leading to aplastic anaemia. This is thought to be due to the formation of a reactive metabolite that causes oxidative stress and DNA damage in bone marrow cells, leading to their depletion. Chloramphenicol's mechanism of action and its potential to cause oxidative stress make it a high-risk medication for causing aplastic anaemia.

**Why Each Wrong Option is Incorrect**
**Option B:** Cephalosporins are a class of beta-lactam antibiotics that work by inhibiting cell wall synthesis in bacteria. They are not typically associated with bone marrow suppression or aplastic anaemia.
**Option C:** Tetracyclines are a class of antibiotics that work by inhibiting protein synthesis by binding to the 30S subunit of the bacterial ribosome. While they can cause various side effects, bone marrow suppression is not a common or well-documented association.
**Option D:** Penicillins are a class of beta-lactam antibiotics that work by inhibiting cell wall synthesis in bacteria. Like cephalosporins, they are not typically associated with bone marrow suppression or aplastic anaemia.

**Clinical Pearl / High-Yield Fact**
It is essential to note that chloramphenicol is rarely used in modern medicine due to its potential for causing aplastic anaemia. When used, it is usually reserved for life-threatening infections where other antibiotics have failed, and the benefits outweigh the risks.

**✓ Correct Answer: A. Chloramphenicol**