In lanthanides, there is poorer shielding of $5 d$ electrons by $4f$ electrons resulting in greater attraction of the nucleus over $5d$ electrons and reduction of the atomic radii.
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.
[Atomic masses $\mathrm{Cu}: 63.54\, \mathrm{u}, \mathrm{S}: 32\, \mathrm{u}, \mathrm{O}: 16 \,\mathrm{u}, \mathrm{H}: 1\, \mathrm{u}]$
${\text{2PQ}} \rightleftharpoons {{\text{P}}_2}{\text{ + }}{{\text{Q}}_2}\,;\,\,\,\,{{\text{K}}_1}{\text{ = 2}}{\text{.5 }} \times \,{\text{1}}{{\text{0}}^5}\,$
${\text{PQ + }}\frac{1}{2}{R_2} \rightleftharpoons PQR\,;\,\,\,\,{{\text{K}}_2}{\text{ = 5 }} \times \,{\text{1}}{{\text{0}}^{ - 3}}\,$
The value of equilibrium constant for reaction
$\frac{1}{2}{{\text{P}}_2}{\text{ + }}\frac{1}{2}{{\text{Q}}_2}{\text{ + }}\frac{1}{2}{R_2} \rightleftharpoons PQR\,$ is