Groundwater of a village is analysed: pH 7.4, fluoride 4.2 ppm, nitrate 30 ppm, lead 20 ppb. Use these standard limits: pH 5.5 to 9.5, fluoride 1 ppm (above 2 ppm is harmful), nitrate 50 ppm, lead 50 ppb. The parameter that makes the water unsafe and the resulting ailment are:

Alead; damage to kidney and brain
Bnitrate; blue baby syndrome
CpH; corrosion of the gut lining
Dfluoride; mottling of teeth and bone deformity

Answer: D

Compare each value with its limit: pH 7.4 is within 5.5 to 9.5, nitrate 30 is below 50 ppm and lead 20 is below 50 ppb. Fluoride at 4.2 ppm is well above 2 ppm, so the water causes dental and skeletal fluorosis.

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