What’s the difference between heterogeneous and homogeneous mixtures?

Mixtures can be either homogeneous or heterogeneous. A mixture in which its constituents are distributed uniformly is called homogeneous mixture, such as salt in water. A mixture in which its constituents are not distributed uniformly is called heterogeneous mixture, such as sand in water.

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).

it is b that is the answer.