Polyatomic ions with identical molecular formula called?

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

Acompound has a molecular weight of 12.124 atomic mass units and the empirical formula c3h40. what is the molecular formula of the compound?

What causes different colors to appear in the sky? the absorption of light by air molecules the reflection of light by bodies of water the greenhouse effect in earth's atmosphere the scattering and reflection of light by dust particles