Deficiency of _______causes a disease known as beri-beri.

The deficiency of Vitamin B1 (Thiamine) causes a disease known as beriberi.

Explanation:
Vitamin B1 (thiamine) is essential for the proper functioning of the nervous system, muscles, and heart. When there is a deficiency of thiamine, the body cannot convert carbohydrates into energy effectively, leading to various symptoms. The condition caused by thiamine deficiency is called beriberi, which manifests in two main forms:

Wet beriberi: This affects the cardiovascular system, leading to symptoms like swelling (edema), rapid heart rate, and shortness of breath due to fluid retention.
Dry beriberi: This affects the nervous system, causing symptoms such as muscle weakness, loss of reflexes, and nerve damage.
Thiamine deficiency is commonly seen in individuals with poor diet, particularly those who rely heavily on polished rice, which lacks thiamine.