Chemistry - f-block Question with Solution | TestHub

Solution:

Let's analyze each element and its characteristics:

(P) Gd (Gadolinium, Z=64): Electronic configuration is $[Xe]4f^{7}5d^{1}6s^2$. It has 8 unpaired electrons ($7$ in $4f$ and $1$ in $5d$), making it paramagnetic. So, P $\to$ 1.

(Q) Tm (Thulium, Z=69): Electronic configuration is $[Xe]4f^{13}6s^2$. It has 1 unpaired electron in $4f$ orbital, making it paramagnetic. Atomic radius generally decreases across the lanthanide series due to lanthanide contraction. Tm is near the end of the series, so it will have a relatively small atomic radius among the given elements. Yb has a smaller radius. So, Q $\to$ 1, 4.

(R) Eu (Europium, Z=63): Electronic configuration is $[Xe]4f^{7}6s^2$. It has 7 unpaired electrons, making it paramagnetic. Due to its half-filled $4f$ subshell, it has a larger atomic radius compared to its neighbors. So, R $\to$ 1, 3.

(S) Yb (Ytterbium, Z=70): Electronic configuration is $[Xe]4f^{14}6s^2$. It has a completely filled $4f$ subshell, meaning no unpaired electrons, making it diamagnetic. It can readily lose two $6s$ electrons to form Yb²⁺, showing a +2 oxidation state. So, S $\to$ 2, 5.

Matching these, we get:

P $\to$ 1

Q $\to$ 1, 4

R $\to$ 1, 3

S $\to$ 2, 5

This matches option B.

The final answer is $\boxed{B}$