Answer: The correct answer (C).
Step-by-step explanation:
Binary compounds: These are the type of chemical compounds which are composed of two different elements. They cannot be further simplified by any chemical methods.
Here , in given option carbon dioxide is a binary compound made up of carbon and oxygen element.
Where as barium and beryllium are pure elements and calcium hydroxide is compound made up of three elements : calcium, hydrogen and oxygen.
So, the correct answer (C).