Write a possible full set of quantum numbers for the electron gained when a bromine atom (br) becomes a bromide ion (br−).

Quantum numbers are a set of numbers used to describe the position and the motion of an electron within the atom.

Quantum numbers are as follows:
n-quantum number : represents the energy level
l-quantum number : represents the orbital (s,p,d,f,)
ml-quantum number : represents the position of the electron within the orbital
ms-quantum number :  represents the spin of the electron within the electron pair.

Bromine has an atomic number of 35.
So, the configuration of the Br is: [Ar] 3d10 4s2 4p5

Now, we will add one electron to the Br to be a negative ion (Br-).
This extra electron will be added to the 4th principle level in the p-orbital.

So, the quantum numbers that represent the extra electron added to the Br will be as follows:
n = 4 (it is added in the 4th principle level)
l = 1 (it is added in the p-orbital)
ml = 1
ms = -1/2