The correct symbol of Iodine with 53 protons and 78 neutrons is shown below.
The symbols comprises two numbers.
Atomic Number:
The number highlighted BLUE is the atomic number of Iodine. Atomic number shows the number o protons present in the nucleus.
Mass Number:
The number highlighted in RED is the mass number of given Iodine. Mass number is the sum of protons and neutrons present in the nucleus. So,
Mass Number = # of Protons + # of Neutrons
Mass Number = 53 + 78
Mass Number = 131
