* Mixture: A mixture is a combination of two or more substances where each substance retains its own properties.

* Heterogeneous Mixture: In a heterogeneous mixture, the components are not evenly distributed throughout. You can usually see the different parts.

* Solution: A solution is a homogeneous mixture where one substance (the solute) dissolves completely into another substance (the solvent).

When you mix baking soda (sodium bicarbonate) and water, the baking soda doesn't fully dissolve. You'll see particles of baking soda suspended in the water, creating a cloudy appearance. This indicates that the mixture is not homogeneous, making it a heterogeneous mixture.

Key Point: While some baking soda does dissolve in water, a significant amount remains as undissolved particles.