Which of the following statements are correct? a) $\mathrm{F}^{-}$ion concentration above $2 \mathrm{ppm}$…
Which of the following statements are correct?
a) $\mathrm{F}^{-}$ion concentration above $2 \mathrm{ppm}$ causes brown mottling of teeth
b) The maximum limit of nitrate in drinking water is $400 \mathrm{ppm}$
c) Depletion of ozone layer leads to cataract and skin cancer
d) The irritant red haze in the traffic is due to oxides of sulphur