Which of the following is not a heavy metal?

The correct answer is Option (4) → Magnesium

Option (1) Lead — A heavy metal. Lead is one of the heavy metals that pollute water.

Option (2) Arsenic — A heavy metal. Arsenic is also a heavy metal found in polluted water.

Option (3) Manganese — A heavy metal. Manganese, too, is a heavy metal that pollutes water.

Option (4) Magnesium — Not a heavy metal. Magnesium is not a heavy metal. Do not confuse it with manganese.

Note: The given answer is as per the official NTA Answer Key. The book does not say in clear words that magnesium is not a heavy metal. It gives lead, arsenic (printed ‘aresenic’), mercury and manganese as heavy metals that pollute water, and magnesium is not among them.