Blue Baby Syndrome is a condition that affects infants and is characterized by a bluish coloration of the skin. It occurs when there is a lack of oxygen in the bloodstream. The correct answer that causes Blue Baby Syndrome is nitrate (NO3).

Option 1: Nitrite (NO2) - Nitrite contamination is not responsible for causing Blue Baby Syndrome. Nitrite poisoning can result in methemoglobinemia, a condition similar to Blue Baby Syndrome, but they are not the same.

Option 2: Sulphite (SO^“) - Sulphite contamination is not linked to Blue Baby Syndrome. Sulphite sensitivity or intolerance can cause adverse reactions in some individuals, but it does not result in the bluish discoloration of the skin.

Option 3: Nitrate (NO3) - This is the correct answer. Nitrate contamination in drinking water can lead to Blue Baby Syndrome. Nitrates can interfere with the ability of red blood cells to carry oxygen, resulting in the bluish appearance.

Option 4: Sulphate (SO^-) - Sulphate is not associated with causing Blue Baby Syndrome. High levels of sulfate in water may have other effects, but not the bluish discoloration seen in Blue Baby Syndrome.