Question

What is the abnormality in the electronic configuration of platinum?

Answer 1

That would speak for [Xe] 4f14 5d8 6s2 if you follow the Aufbau principle (from German Aufbau = setup). But Pt is an exception (as there are some). A rule of thumb is that half-filled shells are stabilized. So that means in the case of Pt [Xe] 4f14 5d9 6s1