Explanation:
It is known that formula for the ionization energy of hydrogen atom is as follows.
E =
or, n =
The value of energy is given as 0.544 eV. Therefore, we will calculate the value of n as follows.
n =
=
= 5
Thus, we can conclude that n equals to 5 for a hydrogen atom if 0.544 eV of energy can ionize it.
Isn't it a because in b at the start of the equation the E in Fe just disappeared
You can simply subtract the atomic number from the mass number in order to find the number of neutrons.
here is an attached photo with a detailed explanation, good luck!