The correct answer is: A. Four atoms
Ethane is a hydrocarbon with the chemical formula $C_2H_6$. It is a colorless, odorless gas that is the main component of natural gas. Ethane is a simple alkane, which means that it is a hydrocarbon that contains only carbon and hydrogen atoms. The carbon atoms in ethane are bonded to each other by single bonds, and each carbon atom is also bonded to two hydrogen atoms. This gives each carbon atom a total of four bonds.
Option B is incorrect because each carbon atom in ethane is bonded to two hydrogen atoms, not one. Option C is incorrect because each carbon atom in ethane is bonded to two hydrogen atoms, not three. Option D is incorrect because each carbon atom in ethane is bonded to two hydrogen atoms, not five.