The correct answer is A. 2, 6.

Propane is a hydrocarbon with the chemical formula $C_3H_8$. This means that it has 3 carbon atoms and 8 hydrogen atoms.

Option B is incorrect because it has 2 carbon atoms and 4 hydrogen atoms.

Option C is incorrect because it has 4 carbon atoms and 7 hydrogen atoms.

Option D is incorrect because it has 3 carbon atoms and 8 hydrogen atoms.