With reference to ‘fuel cells’ in which hydrogen-rich fuel and oxygen are used to generate electricity, consider the following statements : 1) If pure hydrogen is used as a fuel, the fuel cell emits heat and water as by-products. 2) Fuel cells can be used for powering buildings and not for small devices like laptop computers. 3) Fuel cells produce electricity in the form of Alternating Current (AC). Which of the statements given above is / are correct?

The answer is A (1 only). A fuel cell is an electrochemical device, not a combustion engine. Hydrogen and oxygen combine across an electrolyte to give electricity, with water and heat as by-products.

• Statement 1 is correct. With pure hydrogen, the only products are water, heat and electricity. That is why hydrogen fuel cells are called zero-emission at the point of use.
• Statement 2 is wrong. Fuel cells already power buildings as stationary units and as backup power. They also power small devices. Micro direct methanol fuel cells have been developed for laptops and phones, so the restriction to buildings is false.
• Statement 3 is wrong. A fuel cell produces direct current (DC). An inverter is needed to convert it to AC for the grid or household use.

The core concept is electrochemical energy conversion, which is not limited by the Carnot efficiency of heat engines. For Mains GS-3, this links to hydrogen economy, clean energy transition and decentralised power.

Trap: Aspirants often pick D because they assume fuel cells are only for large stationary plants, or they assume that since grid power is AC, fuel cell output must be AC too.