What is being tested when trying to change one substance into another substance

How many miles of calcium oxide will be produced when 1.6 miles of iron (iii) oxide react with calcium phosphate

Consider hydrogen in an excited state n = 5n=5 that emits photons to reach the ground state. there are various possible transitions other than straight to the ground state that can occur; for example, it can drop to the n = 3n=3 state followed by the n = 3n=3 to the ground state transition. which of the possible transitions will result in the emission of a photon in the visible region?

40dm3 of gas at 760 torr are heated from 5°c to 50°c what is the new volume