Efficiency of Carnot engine can be increased by:

Correct option is B

The correct answer is (b) decreasing the sink temperature.
• Carnot efficiency: η = 1 − (T₍cold₎ / T₍hot₎)
• Decrease in sink temperature (T₍cold₎) increases efficiency
• Temperature unit: Kelvin
Information Booster:
• Carnot engine is an ideal heat engine
• Highest possible efficiency
• Independent of working substance
• Efficiency < 100%
Additional Information:
• Increasing sink temperature reduces efficiency
• Real engines have lower efficiency
• Only temperature ratio affects efficiency