Step 1: Recall the chemical (scientific) names paired with the common vitamin labels. Each B-group vitamin and vitamin C has a specific chemical name.
Step 2: Match the options:
Riboflavin = vitamin \( B_2 \).
Thiamine = vitamin \( B_1 \).
Ascorbic acid = vitamin C.
Pyridoxine = vitamin \( B_6 \).
Step 3: The chemical name of vitamin \( B_1 \) is therefore thiamine. A deficiency of vitamin \( B_1 \) (thiamine) causes the disease beri-beri.
\[\boxed{\text{Thiamine}}\]