Read the following passage and answer the next five questions based on it.(32-36)

Battery or cell converts chemical energy of the redox reaction to electrical energy. In fuel cells (a galvanic cell), the chemical energy of combustion of fuels like H2, ethanol, etc., is directly converted to electrical energy. In a fuel cell, H2 and O2 react to produce electricity, where H2
gas is oxidized at the anode and oxygen is reduced at the cathode, and the reactions involved are:

Anode reaction:H₂ + 2OH⁻ → 2H₂O+2e⁻
Cathode reaction:O₂ + 2H₂O +4e⁻ → 4OH⁻

67.2 L of H2 at STP reacts in 15 minutes.

The source of electrical energy on the Apollo moon flight was:

Correct Answer: H2-O2 fuel cell

Explanation:

The passage describes a fuel cell (specifically a galvanic cell) where the chemical energy from the combustion of fuels like $H_2$ and $O_2$ is directly converted into electrical energy.
The anode and cathode reactions given in the passage correspond to the hydrogen-oxygen ($H_2-O_2$) fuel cell.

Historically, the $H_2-O_2$ fuel cell was famously used in the Apollo space program. It served a dual purpose:
1. It provided the primary source of electrical energy for the spacecraft.
2. The byproduct of the cell's reaction is water ($H_{2}O$), which was condensed and used as drinking water by the astronauts during the moon flight.

Therefore, the source of electrical energy on the Apollo moon flight was the H2-O2 fuel cell.