The following are the drawbacks of solar cell panel: (i)    It is costly to set up. (ii)   It is a low power source. (iii)  It is associated with pollution. Option 4 is the correct answer. 

Vegetation that gets submerged and rots under anaerobic conditions produces a large amount of methane gas. Hence, option (3) is correct.

The percentage of methane gas from a typical biogas plant varies between 70% and 75%. 

It is a costly project as it requires land, equipment and high investment for maintenance. The energy potential from the sea (tidal energy, wave energy and ocean thermal energy) is large, but efficient commercial exploitation is difficult. Tidal energy is not likely to be a potential source of energy in the future because there are very few sites around the world which are suitable for building tidal dams.

Black surface absorbs more heat.

Wind is not an exhaustible source of energy.

Gases responsible for greenhouse effect are methane and carbon dioxide, i.e. CH₄ and CO₂. Hence, option (3) is correct.

There are some properties of infrared radiations such as (i)         Heat from the sun is transferred in the form of infrared radiations. (ii)        All hot bodies emit infrared radiations. (iii)       They heat up any body that comes in their path. (iv)       One-third of sunrays is composed of infrared radiations. Thus, options (1), (2) and (4) are properties of infrared radiations. But UV rays are not infrared rays. They are not absorbed by ozone layer in the atmosphere. Therefore, option (3) is not true about infrared radiations.

Ocean thermal energy can be utilised when the temperature difference between water at the surface and water at depths of up to 2 km is 20^o to 25^oC.

Fusion requires temperature about 100 million Kelvin. Pressure squeezes the hydrogen atoms. They must be within 1 x 10^-15 metres of each other to fuse. 

Hydrogen has the highest calorific value of 150 kJ/g.

The energy possessed by rising and falling tides, i.e. the difference in sea levels gives us tidal energy. Hence, option (2) is correct.

Huge amount of wood is required to produce charcoal for commercial and domestic purposes. So, the residue left after burning wood in a limited supply of oxygen is called charcoal. Hence, option (3) is correct.

The element used for interconnection of cells in a solar panel that adds to the cost is silver. Hence, option (3) is correct.

(i)    Fossil fuels are used at a very fast rate. (ii)   Fossil fuels are the remains of plants and animals. They pollute the environment as they are not completely burnt. (iii)  Fossil fuels take a very long time to form as they are the remains of plants and animals which are deeply buried. Option (3) is correct.