Why must an electron absorb a quantum of energy to move to a higher energy level?

For an electron they start at the first level (n=1) I order to move up to the next level (n=2) the amount of quantom energy to move to this next level the energy must be perfect in order to move. If the quantom energy is to small the electron it doesn't try.

> b takes place in the gas phase in an isothermal tubular reactor. the feed is one mole of a per one mole of c, an inert. the entering temperature and pressure are 427°c and 10 atm, respectively. the gas constant r = 0.08206 atm · l/mol · k.