JEE Main · 2019 · 09 Jan 2019 · Shift 2 · Environmental Chemistry

Methaemoglobinaemia, the so-called blue-baby syndrome, is triggered when drinking water carries more than about $50\text{ppm}$ of nitrate. Swallowed nitrate is reduced to nitrite in the gut, and nitrite oxidises the iron of haemoglobin to the ${\text{Fe}}^{3+}$ form, methaemoglobin, which can no longer bind and carry oxygen.