Since 3 positive charges are present in the ion, the number of electrons is less than the number of protons by 3. Let x be the number of electrons. The number of protons is x + 3. The number of neutrons is 0.304x. The mass number is 56. It is equal to the number of protons plus the number of neutrons. 56 = x + 3 + 0.304x
2.304x = 53
x = 23
The number of electrons is 23. The number of protons is 23 + 3 = 26. The number of neutrons is 56 - 26 = 30. The symbol is ⁵⁶₂₆Fe³⁺.