The number of protons in an element is the atomic number of the element, and it is not affected by the charge on the element. Hence, the species which has similar Number of proton is Fe²⁺
To know the species which the same number of protons as Fe³⁺, we need to obtain the <em>atomic number of the elements on the periodic table</em> :
Fe³⁺, Atomic number = 26; Number of protons = 26
Mn³⁺, Atomic number = 25; Number of protons = 25
Co²⁺, Atomic number = 27; Number of protons = 27
Fe²⁺, Atomic number = 26; Number of protons = 26
Ni, Atomic number = 28; Number of protons = 28
Therefore, only Fe²⁺ has the same number of protons as Fe³⁺
