Answer:
Initial state    Final state
      3           ⇒        2
      3           ⇒        1
      2          ⇒         1
Explanation:
For this exercise we must use Bohr's atomic model
          E = - 13.606 / n²
where is the value of 13.606 eV is the energy of the ground state and n is the integer.
The energy acquired by the electron in units of electron volt (eV)
           E = e V
           E = 12.5 eV
all this energy is used to transfer an electron from the ground state to an excited state
         ΔE = 13.6060 (1 / n₀² - 1 / n²)
the ground state has n₀ = 1
        ΔE = 13.606 (1 -  1/n²)
         1 /n² = 1 - ΔE/13,606
          1 / n² = 1 - 12.5 / 13.606
          1 / n² = 0.08129
           n = √(1 / 0.08129)
           n = 3.5
  since n is an integer, maximun is
          n = 3
because it cannot give more energy than the electron has
 From this level there can be transition to reach the base state.
  
Initial state    Final state
      3           ⇒        2
      3           ⇒        1
      2          ⇒         1