Chemistry - PERIODIC TABLE Question with Solution | TestHub

The correct order is Ni < Pd < Pt for first ionisation energy. Due to the lanthanide contraction, Pt has a smaller size and a higher effective nuclear charge than expected, so its ionisation energy is higher than that of Pd and Ni.

A. 7s and 4f have the same n+l value (7), so the orbital with the lower n has the lower energy: 4f < 7s. The order 7s < 4f is incorrect.

B. The first ionisation energy order is Sc > Y > La, so Sc > Y = La is incorrect.

C. Ni < Pd < Pt is correct.

D. The penetration power order is 3s > 3p > 3d, so 3d > 3p > 3s is incorrect.