Match the following columns with respective positions of centre of...

(A) Uniform rod of length $R$ - For a uniform rod, the COM lies exactly at the midpoint. So, (x=$\frac{R}{2}$). That matches (Q). (B) Uniform thin semicircular ring of radius R - Standard result: COM of a semicircular ring lies at a distance ($\frac{2 R}{\pi}$) from the center, along symmetry axis. So, (x=$\frac{2 R}{\pi}$). That matches (S). (C) Uniform semicircular disc of radius R - Standard result: COM of a semicircular lamina is at a distance ($\frac{4 R}{3 \pi}$) from the center along symmetry axis. So, (x=$\frac{4 R}{3 \pi}$). That matches (R). (D) Uniform solid hemisphere of radius R - Standard result: COM of a solid hemisphere is at a distance ($\frac{3 R}{8}$) from the flat face (base). So, (x=$\frac{3 R}{8}$). That matches (P).