Air pollution is not caused by
(a) Pollen grains
(b) Hydroelectric power
(c) Industries
(d) Automobiles

Options

A. Pollen grains
B. Hydroelectric power
C. Industries
D. Automobiles

Answer

To solve the question "Air pollution is not caused by", we need to analyze each option provided:

1. **Pollen grains**:
- Pollen grains are microscopic particles released by plants during their reproductive cycle. While they can cause allergic reactions in some individuals, they are not considered a significant source of air pollution in the same way that industrial emissions or vehicle exhausts are. Therefore, they do not contribute to air pollution in a harmful way.

2. **Hydroelectric power**:
- Hydroelectric power is generated by harnessing the energy of flowing water to produce electricity. This method of energy production does not involve the burning of fossil fuels or the release of harmful pollutants into the air. Hence, hydroelectric power does not cause air pollution.

3. **Industries**:
- Industries are known to be significant contributors to air pollution. They emit various pollutants, including oxides of carbon, sulfur, and nitrogen, as well as particulate matter. These emissions can have detrimental effects on air quality and public health.

4. **Automobiles**:
- Automobiles are another major source of air pollution. They release exhaust gases, including carbon monoxide, nitrogen oxides, and hydrocarbons, which contribute to the degradation of air quality.

Based on this analysis, the option that does not cause air pollution is:

**Answer: (b) Hydroelectric power**