(a) Charcoal is considered to be a better fuel than wood because:

1. It burns without flames.
2. It is comparatively smokeless.
3. It has higher calorific value, i.e. higher heat generating efficiency than wood.

(b) Biogas plant helps to reduce the problem of pollution in the following ways.

1. It provides better sanitation due to safe disposal of bio-waste and sewage material.
2. Biogas obtained from this plant produces less smoke on burning.
3. The residue left can be used as a manure which can be used as an alternative of fertilizers. Thus, it prevents soil and water from degradation.