Which one of the following statements is not true for hydropower generated from river dams?
(1) Dams encourage sustainable growth.
(2) It does not pollute water or air.
(3) Hydropower facilities can have large environmental impacts.
(4) Dams displace indigenous people from their river lifelines.

Which one of the following is responsible for turning Taj Mahal yellow?

Correct Answer: Sulphur dioxide

Explanation:

The yellowing of the Taj Mahal is primarily caused by atmospheric pollution, specifically acid rain and particulate matter.

1. Role of Sulphur Dioxide (SO₂): Industries and refineries located in and around the Agra region (such as the Mathura Oil Refinery) emit large quantities of sulphur dioxide (SO₂) and nitrogen dioxide (NO₂) into the air.

2. Formation of Acid Rain: Sulphur dioxide reacts with water vapor, oxygen, and other chemicals present in the atmosphere to form sulphuric acid (H₂SO₄).

${\text{SO}}_2+{\text{H}}_2\text{O}+½{\text{O}}_2\to {\text{H}}_2{\text{SO}}_4$

3. Reaction with Marble: The Taj Mahal is made of white marble, which is composed of calcium carbonate (CaCO₃). When acid rain containing sulphuric acid falls on the marble, it reacts to form calcium sulphate (gypsum).

${\text{CaCO}}_3+{\text{H}}_2{\text{SO}}_4\to {\text{CaSO}}_4+{\text{H}}_2\text{O}+{\text{CO}}_2$

This reaction gradually corrodes and discolors the marble, turning its pristine white color into a yellowish hue (often referred to as "Marble Cancer").

Therefore, Sulphur dioxide is the main substance responsible for turning the Taj Mahal yellow.