How do i find mass when not given in chemistry

What is a possible quantum number set for an electron in the 3s orbital of a magnesium atom

Read the chemical equation. 2c2h2 + 5o2 → 4co2 + 2h2o which of the following statements would be correct if one mole of c2h2 was used in this reaction? one mole of oxygen was used in this reaction. five moles of oxygen were used in this reaction. four moles of carbon dioxide were produced from this reaction. two moles of carbon dioxide were produced from this reaction.

What is a difference between a mixture of elements and a mixture of compounds