Here's why:

* Homogeneous mixtures have a uniform composition throughout. This means that the salt is evenly distributed in the water, and every part of the solution has the same concentration of salt.

* Heterogeneous mixtures have visible, distinct parts. You can easily separate the components of a heterogeneous mixture.

When you dissolve salt in water, the salt crystals break down and the individual ions (sodium and chloride) become surrounded by water molecules. You can't see the salt particles anymore, and the solution looks clear. This uniform composition makes it a homogeneous mixture.