Final answer:
In a gas boiler, chemical energy from the fuel is converted into thermal energy, which is used to heat water and subsequently a home.
Step-by-step explanation:
When considering a gas boiler, the energy transformations involve the conversion of chemical energy to thermal energy. The fuel's chemical energy is released when it burns. This energy then heats water in the boiler's pipes, and the heated water can be used to warm a home. The byproduct of combustion, which includes hot exhaust gas, represents a loss of energy to the surroundings. Therefore, among the options provided, the correct one is that chemical energy is converted to thermal energy.