Many thermal plants are set up near coal or oil fields because:

1. Fuel Availability: Thermal power plants primarily rely on coal or oil as fuel for generating electricity. Setting up plants near coal or oil fields reduces transportation costs and ensures a steady and reliable supply of fuel to the power plants.

2. Efficiency: Proximity to coal or oil fields allows for efficient extraction and transportation of fuel to the power plants, minimizing losses associated with fuel transportation and storage.

3. Infrastructure: Coal or oil fields often have existing infrastructure such as railways, pipelines, and storage facilities, which can be utilized for transporting fuel to thermal power plants, thereby reducing initial setup costs and time.

(a) Four gases mainly present in biogas are methane (CH4), carbon dioxide (CO2), hydrogen (H2), and traces of hydrogen sulfide (H2S). (b) Advantages of using biogas over fossil fuels include:

1. Renewable: Biogas is produced from organic waste materials such as animal dung, crop residues, and kitchen waste, which are continuously generated and can be replenished naturally.
2. Environmentally Friendly: Biogas production reduces methane emissions from organic waste decomposition and displaces the use of fossil fuels, contributing to reduced greenhouse gas emissions and mitigating climate change.

Hazards of nuclear waste include:

1. Radioactive Contamination: Nuclear waste contains radioactive isotopes that emit harmful ionizing radiation, posing health risks to living organisms and the environment.
2. Long-term Storage: Nuclear waste remains hazardous for thousands of years and requires secure long-term storage facilities to prevent accidental exposure and contamination.
3. Nuclear Proliferation: Improper handling and disposal of nuclear waste can increase the risk of nuclear proliferation and the potential for nuclear accidents or terrorist attacks.