Incorrectly matched pair:
b) Vitamin B6 - Loss of appetite

Explanation:

Vitamin B6, also known as pyridoxine, is an essential water-soluble vitamin that plays a crucial role in various bodily functions. It is involved in the metabolism of amino acids, carbohydrates, and lipids, and is also necessary for the proper functioning of the nervous system. However, loss of appetite is not a specific symptom associated with vitamin B6 deficiency.

Correctly matched pairs:
a) Vitamin B12 - Pernicious anaemia
c) Vitamin B1 - Beri-beri
d) Vitamin B3 - Pellagra

Explanation of correct matches:

a) Vitamin B12 - Pernicious anaemia:
Vitamin B12 is required for the production of healthy red blood cells and the proper functioning of the nervous system. Pernicious anaemia is a condition characterized by the inability of the body to absorb vitamin B12 from the gastrointestinal tract, leading to a deficiency of this vitamin. Symptoms of vitamin B12 deficiency include weakness, fatigue, pale skin, shortness of breath, and neurological problems.

c) Vitamin B1 - Beri-beri:
Vitamin B1, also known as thiamine, is essential for the metabolism of carbohydrates and the proper functioning of the nervous system. Deficiency of vitamin B1 can lead to a condition called beri-beri, which is characterized by symptoms such as weakness, fatigue, muscle pain, confusion, and difficulty walking.

d) Vitamin B3 - Pellagra:
Vitamin B3, also known as niacin, is important for energy production, DNA repair, and the metabolism of fats and carbohydrates. Pellagra is a condition caused by a severe deficiency of vitamin B3. It is characterized by the "4 D's": dermatitis (skin rash), diarrhea, dementia, and death if left untreated.

Overall, the pair that is not correctly matched is b) Vitamin B6 - Loss of appetite. While loss of appetite can occur in certain conditions, it is not a specific symptom of vitamin B6 deficiency.