The disease caused by a deficiency of protein in children is

Correct answer: (a) Marasmus

Explanation

Marasmus is a severe protein-energy malnutrition in children caused by deficiency of protein and calories, leading to wasting.

Pellagra results from niacin (vitamin B3) deficiency, Beri-beri from thiamine (vitamin B1), and Rickets from vitamin D deficiency.

Therefore the protein-deficiency disease of children is Marasmus.