'Blue baby syndrome' is due to the presence of which of the following in the blood ?

Blue baby syndrome, medically known as methemoglobinemia, is a condition characterized by a reduced ability of the blood to carry oxygen. It typically occurs when infants ingest water or food contaminated with high levels of nitrates. In the digestive system, these nitrates are converted into nitrites, which then enter the bloodstream and react with haemoglobin to form methemoglobin. Unlike normal haemoglobin, methemoglobin is unable to release oxygen effectively to body tissues. This lack of oxygen causes the skin to develop a bluish tint (cyanosis). While nitrate is the environmental contaminant that triggers the process, the actual substance present in the blood that causes the syndrome is methemoglobin.