One photon is emitted each time an electron downs one or more levels of energy.
The ground state of hydrogen is n = 1.
So the electron has the possibility to release one photon when the electrons goes downward from n = 4 to n = 3, one more photon when goes downward from n = 3 to n = 2 and one more photon when goes downward from n = 2 to n = 1. So, the largest number of photons that can be emiited as the atom returns fo the ground state (n = 1) is 3.
Answer: 3
