Question

which is one physical property that all stars have?
they are made of gases.
they shine very brightly.
they have a triangle shape.
they contain iron in their cores.

Explanation:

Stars are large celestial bodies composed mainly of hydrogen and helium gases. Not all stars shine very brightly (e.g., some are dim red dwarfs). Stars are spherical (not triangle - shaped). While some stars may have iron in their cores at certain stages (like in the later stages of massive stars), it is not a property of all stars. But being made of gases is a fundamental property of all stars.

Answer:

A. They are made of gases.