Which one of the following has electronic configuration in violation of Aufbau

principle?

a) calcium b) titanium c) chromium d) manganese

Chromium violates aufbau principle. This is bcoz aufbau principle says that electrons should first b filled in orbitals hving lower energy so Cr should hav 3d4 4s2 configuration. But here 1 electron migrate and 3d5 4s1 is seen experimentally. This tends to half filled d orbitals having greater stability and greater exchange energy. Thus it violates the law. Hope u got it and pl approve if u like it.