Chemistry - PERIODIC TABLE Question with Solution | TestHub

(A) ns < np < nd < nf (penetration power) Incorrect

Penetration power actually follows: $ns>np>nd>nf$

Because s-orbitals penetrate closest to the nucleus.

So the given order is wrong.

(B) Li < Na < K < Cs (Zₑff order) Incorrect

This is actually the **atomic radius trend**, not effective nuclear charge ($Z_{eff}$).

$Z_{eff}$ generally increases across a period, not down a group.

So the statement is incorrect.

(C) Sc < Y < La (atomic radius order) Correct

Atomic size increases down the group due to the addition of shells.

scandium < yttrium < lanthanum

(D) Sc > Y > La (ionisation energy order) Correct

Ionization energy decreases down the group due to increasing atomic size and shielding.