Question

chemotrophs can then use as energy. unlike the more common autotrophs and heterotrophs, chemotrophs make up much less of earths biodiversity. these unique organisms contribute to our understanding of the vast and diverse array of life forms that exist on earth. where do chemotrophs get their energy from? sunlight chemical compounds molten lava

Explanation:

The text mentions that chemotrophs use something as energy. Autotrophs use sunlight (which is why option A is wrong as chemotrophs are different). Molten lava isn't a source of energy for organisms in a typical sense related to their metabolic energy - gathering. Chemotrophs, by definition, obtain energy from chemical compounds.

Answer:

B. chemical compounds