* Mass Number: The mass number represents the total number of protons and neutrons in an atom's nucleus.

* Number of Electrons: In a neutral atom, the number of electrons is equal to the number of protons.

Steps:

1. Find the number of protons: Since the atom is neutral, the number of protons is equal to the number of electrons, which is 45.

2. Find the number of neutrons: Subtract the number of protons (45) from the mass number (103): 103 - 45 = 58 neutrons.

3. Identify the element: The element with 45 protons is Rhodium (Rh).

Therefore, the element with a mass number of 103 and 45 electrons is Rhodium (Rh).