Answer: The correct option is 3.
Explanation: Binary compounds are the compounds which are formed by the combination of 2 elements.
We are given some options, from that only 1 option is satisfying the definition of binary compounds, which is carbon dioxide [tex](CO_2)[/tex]
Carbon dioxide is made from the combination of two elements which are oxygen and carbon.
Option 1 and 2 are the elements.
Option 4: Calcium hydroxide [tex](Ca(OH)_2)[/tex] is a compound made from the combination of more than 2 compounds which are calcium, hydrogen and oxygen. Hence, it cannot be considered as a binary compound.
Hence, the correct option is 3.
