Answer
Please see the work below.
Work Step by Step
The first transition series or 3d series consists of 9 elements from Scandium to Copper.
Their atomic numbers and electronic configurations can be represented as follows,
Scandium, Sc – atomic number – 21.
Electronic configuration - $1s^{2} 2s^{2}2p^{6} 3s^{2}3p^{6}3d^{1}4s^{2}$
Titanium, Ti – atomic number – 22.
Electronic configuration - $1s^{2} 2s^{2}2p^{6} 3s^{2}3p^{6}3d^{2}4s^{2}$
Vanadium, V – atomic number – 23.
Electronic configuration - $1s^{2} 2s^{2}2p^{6} 3s^{2}3p^{6}3d^{3}4s^{2}$
Chromium, Cr – atomic number – 24.
Electronic configuration - $1s^{2} 2s^{2}2p^{6} 3s^{2}3p^{6}3d^{5}4s^{1}$
Magnesium, Mn – atomic number – 25.
Electronic configuration - $1s^{2} 2s^{2}2p^{6} 3s^{2}3p^{6}3d^{5}4s^{2}$
Iron, Fe – atomic number – 26.
Electronic configuration - $1s^{2} 2s^{2}2p^{6} 3s^{2}3p^{6}3d^{6}4s^{2}$
Cobalt, Co – atomic number – 27.
Electronic configuration - $1s^{2} 2s^{2}2p^{6} 3s^{2}3p^{6}3d^{7}4s^{2}$
Nickel, Ni – atomic number – 28.
Electronic configuration - $1s^{2} 2s^{2}2p^{6} 3s^{2}3p^{6}3d^{8}4s^{2}$
Copper, Cu – atomic number – 29.
Electronic configuration - $1s^{2} 2s^{2}2p^{6} 3s^{2}3p^{6}3d^{10}4s^{1}$
From the electronic configurations, it is clear that the configurations of the inner shell remain the same and there is a difference in the configurations of the valence shell and penultimate shell.
Hence the general configurations can be represented as $(n-1)d^{1-10}ns^{1-2}$
