Question

Which one among the following is a transition element that occurs when the inner $3d$ orbitals is partially filled.

• A. Fe
• B. Au
• C. Na
• D. Ar
• E. U

Answer 1

The correct option is A Fe

Iron (Fe) is a transition element that occurs when the inner 3d orbitals is partially filled.
The electronic configuration of iron is $1s^{2}2s^{2}2p^{6}3s^{2}3p^3{d}^{6}4s^2$.
Thus, inner 3d orbital has only 6 electrons. Maximum 10 electrons can be accommodated in 3d orbital. Hence, 3d orbital is partially filled.