Question

Underline/Select the word which does not belong to the group: carbon dioxide, carbon, hydrogen, carbon monoxide.

Answer 1

carbon dioxide ,carbon ,carbon monoxide are same family

your answer is hydrogen

Answer 2

Carbon does not belong to this group.

The reason is that carbon dioxide, hydrogen, carbon monoxide is gasses but carbon is a solid element.  

This is why it does not belong to the same category.

Carbon has the ability to make 4 bonds that is why it exists in many different forms.