A solar water heater cannot be used to get hot water on:

Ans: Option B - Cloudy day

A solar water heater uses the Sun's energy to heat water. To function correctly, it requires bright and intense Sunshine. On a cloudy day, Sunlight is reflected back into the sky by the clouds, preventing it from reaching the ground. As a result, solar energy is not available for the solar heater to function correctly. As a result, on a cloudy day, the solar water heater will not work.