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.
A binary compound is a compound that contain two different chemical elements in it. These compounds may be molecular or may also exist in other forms such as solid. In this case Barium and Beryllium are not binary compounds since they are independent elements, Calcium hydroxide is also not a binary compound since it has more than two chemical elements. Therefore,carbon dioxide is the binary compound since it contains two chemical elements ( carbon and oxygen)
