Which substance is a binary compound? 1. barium 2. beryllium 3. carbon dioxide 4. calcium hydroxide?

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

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 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.

i just learnt this recently but i need to look through my notes again

the answer is d.) potassium