An element has a unique number of protons in its atom.
The Periodic Table of Elements is composed of 118 elements
A chemical element is a substance that cannot be further broken down by any chemical reaction
A chemical compound is formed by the chemical union of two or more elements in a fixed ratio.
Baking soda (Sodium Bicarbonate) is composed of 1 Na, 1 H, 1 C, and 3 O, NaHCO3
Re-read the prompt... Baking soda is heated, a gas is formed, and solid remains having less mass than it started with, and does not have the same properties as the original sample.
Baking soda is not an element, it is a compound.