Final answer:
A mixture of flour and water does not dissolve into a uniform substance, thus it is known as a heterogeneous mixture.
Step-by-step explanation:
A mixture of flour and water is called a heterogeneous mixture because the substances do not dissolve and create a non-uniform mixture. Each substance retains its own properties and can be visibly distinguished when mixed. In contrast, a homogeneous mixture refers to a mixture that has a uniform composition throughout, like salt dissolved in water, and appears as a single substance.