Explanation:

- Pernicious anaemia is caused by a deficiency of vitamin B12.

- Vitamin B12 is crucial for red blood cell production and nerve function.

- A lack of vitamin B12 affects the body's ability to produce healthy red blood cells, leading to pernicious anaemia.

- Option: 1, B2 (Riboflavin)

- Riboflavin is essential for energy production and cellular function.

- Its deficiency is not linked to pernicious anaemia.

- Option: 2, B6 (Pyridoxine)

- B6 is vital for protein metabolism and cognitive development.

- Its deficiency causes other forms of anaemia, but not pernicious anaemia.

- Option: 3, B1 (Thiamine)

- Thiamine is important for energy metabolism and nerve function.

- Its deficiency leads to beriberi, not pernicious anaemia.

- Option: 4, B12 (Cobalamin)

- A lack of B12 leads directly to pernicious anaemia due to its role in red blood cell formation and DNA synthesis.