The number of ‘d’ electrons in Fe²⁺ is not equal to that of

Electronic configuration of the elements are:

Fe²⁺:1s²2s²2p⁶3s²3p⁶3d⁶

number of d-electrons=6

Fe²⁺:1s²2s²2p⁶3s²3p⁶4s²3d⁶-has 6 electrons in d-orbital i.e. same as in d- robital of Fe²⁺

Ne:1s²2s²2p⁶-has 6 electrons in p-orbital i.e. same as in d- robital of  Fe²⁺
 

Mg:1s²2s²2p⁶3s²-has (2+2+2) 6 electrons in s-orbital i.e. same as in d- robital of Fe2+
 

Cl:1s²2s²2p⁶3s²3p⁵-has (6+5) 11 electrons in p-orbital and are not same as in d- orbital of Fe²⁺.