Here it is to calculate the energy of an electron found in the second shell of the hydrogen atom. Alright, since we're looking for the energy of an electron within a given shell, we're looking for its potential energy, its energy of position.
So ΔE=-R∗Z2/N2. R is our Ryberg constant, so that's -2.178∗10-18 J. Z equals the atomic number of the element. Since it's hydrogen, its atomic number is 1, so that would be 12/N2. Remember N here is the energy level or shell number. They tell us it's the second shell, so N = 2, so that would be 22.
So here that's -2.178∗10-18 J. 12 is just one. 22 is 4, so that comes out to -5.445∗10-19 J. Since it doesn't give us a number of sig figs in the beginning of the question at all, we can determine our own number of sig figs here. I'm just going with four significant figures in terms of the potential energy for that particular electron.