Correct Answer - Option 2 : Supplying the intake of an engine with air at a density greater than the density of the surrounding atmosphere
Supercharging is the process of supplying air or fuel-air mixture higher than the pressure at which engine naturally aspirates i.e. atmosphere.
The objective of supercharging:
(i) To increase the power output for a given weight and bulk of the engine. This is important for aircraft, marine and automotive engine where weight and space important.
(ii) To compensate for the loss of power due to attitude. This mainly relates to aircraft engines which lose power at an approximate rate of one per cent 100 metres altitudes. This is also relevant for other engines which are used at high altitudes.
(iii) To obtain more power from an existing engine.