How to remember exceptional case of electronic configuration of transition element

Exceptional cases of electronic configuration.
The electronic configuration depends upon stability. Exceptions are related with half-filled and fully filled subshells that are more stable.
Trick:
Look carefully last 2 subshell of transition metal (n-1d) ns, if d orbital becomes  half-filled and completely filled by moving 1 electron from s orbital then transition element will follow exceptional case.
E.g.:  Cr having atomic number 24
Expected: 1s2 2s2 2p6 3s2 3p6 3d4 4s2
Actual:   1s2 2s2 2p6 3s2 3p6 3d5   4s1                 
Other examples are given below
Copper [Ar] 3d10 4s1
 Molybdenum [Kr] 4d5 5s1
 Silver [Kr] 4d 10 5s1
Gold [Xe] 4f14 5d10 6s1

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