Here's why:

* Element: A pure substance that cannot be broken down into simpler substances by chemical means. Examples: oxygen (O), carbon (C), gold (Au).

* Compound: A substance formed when two or more different elements are chemically combined in a fixed ratio. Examples: water (H₂O), carbon dioxide (CO₂).

Baking soda (NaHCO₃) is made up of the elements sodium (Na), hydrogen (H), carbon (C), and oxygen (O). It's not a single element, but a combination of them.