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Which of the following statements are not correct?
(i) \( \mathrm{F}^{-} \)ion concentration above \( 2 \mathrm{ppm} \) causes brown mottling in teeth.
(ii) Excessive \( \mathrm{F}^{-} \)(over \( 10 \mathrm{ppm} \) ) causes harmful effect to bones and teeth.
(iii) Excessive lead in drinking water causes disease methemoglobinemia
(iv) Deficiency of sulphate in drinking water causes laxative effect.
(a) (ii) and (iv)
(b) (ii) and (iii)
(c) (ii), (iii) and (iv)
(d) (iii) and (iv)
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