Which of the below mentioned is a compound?

When two hydrogen atoms join with two oxygen atoms that have already bonded, hydrogen peroxide is created. 

Octane is a hydrogen and carbon-based hydrocarbon. 

Sodium bicarbonate (baking soda) is made when carbon dioxide reacts with an aqueous solution of sodium hydroxide to form sodium carbonate, which is then mixed with carbon dioxide molecules to form sodium bicarbonate. 

All compounds are made up of various elements and have properties that differ from those of their constituent elements.