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

* Charge and Electrons: The charge of an ion tells us how many electrons it has gained or lost compared to a neutral atom. A +1 charge means it has lost one electron.

* Protons and Electrons: In a neutral atom, the number of protons (atomic number) equals the number of electrons.

Let's break it down:

1. Finding the Number of Protons: Since the ion has a +1 charge, it has lost one electron. This means it originally had 105 + 1 = 106 electrons. In a neutral atom, the number of electrons equals the number of protons. Therefore, it has 106 protons.

2. Calculating the Mass Number:

Mass Number = Protons + Neutrons

Mass Number = 106 + 157 = 263

Therefore, the mass number of this ion is 263.