The correct answer is Carbon dioxide (CO₂).![image](//cdn. Points

• Carbon dioxide (CO₂) is an acidic gas present in the atmosphere.

• When CO₂ dissolves in rainwater, it reacts with water to form carbonic acid (H₂CO₃).

• This process occurs naturally and contributes to the slightly acidic nature of rainwater, with a typical pH of around 5.6.

• Carbonic acid is a weak acid and does not cause significant environmental damage under normal conditions.

• The reaction is represented as: CO₂ + H₂O ⇒ H₂CO₃.![image](//cdn. Information**

• Nitrogen (N₂)

• Nitrogen makes up about 78% of Earth's atmosphere but is inert under normal conditions.

• It does not dissolve in rainwater to form any acid under normal circumstances.

• Nitrogen oxides (NO and NO₂) can dissolve in rainwater to form nitric acid (HNO₃), contributing to acid rain, but these are not directly produced by nitrogen gas (N₂).

• Oxygen (O₂)

• Oxygen constitutes approximately 21% of the Earth's atmosphere and is essential for life.

• It does not form acids when dissolved in rainwater.

• Oxygen is involved in oxidation processes but does not contribute directly to the acidity of rainwater.

• Sulfur dioxide (SO₂)

• Sulfur dioxide is a major contributor to acid rain, as it reacts with water to form sulfurous acid (H₂SO₃) and further oxidizes to form sulfuric acid (H₂SO₄).

• It is primarily released into the atmosphere through industrial activities, burning fossil fuels, and volcanic eruptions.

• Sulfur dioxide's role is significant in environmental pollution and acid rain formation.