For a proton, the charge is represented by +e
For an electron, the charge is represented by -e
The charge of an electron [e] is equal to the - 1.602 * 10^-19 Coulombs
For an ionized atom, the net charge is equal to the sum of charges in the proton and the electron in that atom.
From the question, we are told that, the iron atom has 26 protons and 7 electrons.
The net charge Q = 26 [ +e] + 7 [- e] = +19 e
+19 e = + 19 [1.602 * 10^-19 C] = + 3.04 * 10^-18 C.
