Questions

No work done as there is no external external pressure in free expansion. 

Hence, Work done in a free expansion process is Zero.

Bicycle is a compound machine in the above given options. A compound machine is a machine that is formed by two or more simple machines.

Plants are producers, which means they make their own food. Chloroplasts are organelles found in eukaryotic and plant cells that conduct photosynthesis. Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide gas to produce food for the plant.

Plants use energy from sunlight to help make their food, but they need chloroplasts to do it.

Hence, in plants, chloroplasts are necessary for Photosynthesis.

Chemical weathering is what happens when rocks are broken down and chemically altered.

Chemical weathering is the breakdown of rocks by chemical reactions. Chemical weathering involves changes in the chemical composition of the existing rock to form new rock. Some examples of chemical weathering are hydrolysis, oxidation, carbonation, dissolution, etc.

A fossil is a traces or remainings of plants and animals that lived in the past. The fossil record provides evidence of a common ancestor to many species is the option that best describes the fossil record.

Electrical discharge machining (EDM), also known as spark machining, spark eroding, burning, die sinking, wire burning or wire erosion, is a manufacturing process whereby a desired shape is obtained by using electrical discharges.

Tractor was the single most important invention to farmers.