In an engine, if fuel economy is desired, there must be:

Correct option is C

✅ (c) An excess of both fuel and oxygen: • For fuel economy, optimal air-fuel ratio is essential – this includes adequate oxygen for complete combustion. • Slight excess of oxygen ensures complete combustion of fuel, reducing fuel wastage and improving efficiency. • Complete combustion releases maximum energy and reduces emissions.
❌ (a): • Leads to incomplete combustion, causing carbon deposits and pollution.
❌ (b): • Without enough fuel, the engine cannot generate required power.
❌ (d): • Incorrect, as (c) is the best choice for fuel economy.