James Watt discovered the energy of steam.

The correct passive voice sentence is:

"The energy of steam was discovered by James Watt."

Explanation:

• "The energy of steam was discovered by James Watt." correctly uses the passive voice to indicate that James Watt was the one who discovered the energy of steam.

Here’s why the other options are incorrect:

"James Watt discovered the energy of steam." This is the active voice form of the sentence, not the passive voice.

"The energy of Steam discovered James Watt." This sentence incorrectly suggests that the energy of steam did the discovering, which is not logical.

"James Watt was discovered by the energy of steam." This incorrectly implies that James Watt was discovered by the energy of steam, which is not what the original sentence means.

"James Watt had discovered energy by the steam." This is not a correct passive construction and also misrepresents the intended meaning.