Correct Answer - Option 4 : iron, manganese and magnesium
The metals found in natural water are classified in toxic and non-toxic metals.
Toxic metals are: Cadmium (Cd), lead (Pb), Mercury (Hg), Silver (Ag), Arsenic (As) and Barium (Ba).
Non-Toxic are:
Sodium (Na) - Permissible value – 50 -250 mg/l
Copper (Cu) - Permissible value – 0.05 to 1.5 mg/l
Calcium (Ca) - Permissible value up to 60 mg/l
Zinc (Zn) – Permissible value - 5-15 mg/l
Manganese (Mn) - Permissible value – 0.05 – 0.5 mg/l
Magnesium (Mg) - Permissible value - up to 40 mg/l
Iron (Fe) - Permissible value- 0.1-1 mg/l