Which one of the following pairs is not correctly matched : -

Vitamin C (ascorbic acid) deficiency causes scurvy (bleeding gums, poor wound healing); correctly matched.
Vitamin $B_{12}$ (cyanocobalamin) deficiency causes pernicious anaemia; correctly matched.
Beri-beri is caused by deficiency of vitamin $B_1$ (thiamine). Vitamin $B_6$ (pyridoxine) deficiency causes dermatitis, anaemia and convulsions. So 'Vitamin $B_6$ – Beri-beri' is not correctly matched.
As per the answer key, the pair not correctly matched is Vitamin $B_6$ – Beri-beri.
Note: 'Vitamin $B_2$ – Pellagra' is also not strictly correct, since pellagra is caused by deficiency of niacin (vitamin $B_3$), while riboflavin ($B_2$) deficiency causes cheilosis and glossitis. The answer key gives $B_6$ – Beri-beri, which is the clearly wrong pair.