The transition elements have a characteristic electronic configuration which can be represented as:

• A
  $(n - 2)s^2p^6d^{1-10} (n - 1)s^2p^6 ns^2$
• B
  $(n - 2)s^2p^6d^{1-10} (n - 1)s^1p^6d^1 \text{ or } d^1ns^1$
• C
  $(n - 1)s^1p^6d^{10}ns^2p^6nd^{1-10}$
• D
  $(n - 1)s^2p^6d^{1-10}ns^1 \text{ or } ns^2$