These are transition metals so first two electrons will free from s subshell then electrons start getting out from d subshell so Fe +2 has one paired and 4 unpaired electrons in outer most shell but in hybridization it can use 6 electrons to make bond with other atoms. but nickel can use 7 electrons to make bond ................................so what do you think who is best

The maximum number of unpaired electrons in transition metal ions can be determined by looking at their electron configurations. Transition metals have partially filled d orbitals, which can give rise to unpaired electrons.

a. Fe2+ (Iron ion with a 2+ charge):
The electron configuration of Fe2+ is [Ar] 3d6. The 3d subshell has a maximum capacity of 10 electrons. Since Fe2+ has 6 electrons in the 3d subshell, there are 4 unpaired electrons.

b. Ni3+ (Nickel ion with a 3+ charge):
The electron configuration of Ni3+ is [Ar] 3d7. Similar to Fe2+, the 3d subshell has a maximum capacity of 10 electrons. With 7 electrons in the 3d subshell, there are 3 unpaired electrons.

c. Cu2+ (Copper ion with a 2+ charge):
The electron configuration of Cu2+ is [Ar] 3d9. Again, the 3d subshell can hold up to 10 electrons. However, in the case of Cu2+, one electron from the 4s subshell moves to the 3d subshell to create a more stable half-filled 3d subshell. As a result, there is only 1 unpaired electron in Cu2+.

d. Zn2+ (Zinc ion with a 2+ charge):
The electron configuration of Zn2+ is [Ar] 3d10. In this case, the 3d subshell is completely filled with 10 electrons. Therefore, there are no unpaired electrons in Zn2+.

In summary:

a. Fe2+ has 4 unpaired electrons.
b. Ni3+ has 3 unpaired electrons.
c. Cu2+ has 1 unpaired electron.
d. Zn2+ has no unpaired electrons.

The number of unpaired electrons determines the magnetic properties and reactivity of transition metal ions. Transition metal ions with unpaired electrons are generally more reactive and can exhibit paramagnetic behavior due to the presence of unpaired spins. On the other hand, transition metal ions with no unpaired electrons are less reactive and diamagnetic, meaning they are not attracted to a magnetic field.