a
When a ray light travels from \(\mu_{1}\) to \(\mu_{2}\) after refraction at a single curved surface,

\(\frac{\mu_{2}}{v}-\frac{\mu_{1}}{u}=\frac{\mu_{2}-\mu_{1}}{R}\)

As per sign convention,

\(u=-x, v=+x, R\) is \(+v e\)

\(\mu_{1}=1, \mu_{2}=1.5\)

\(\therefore \frac{1.5}{x}-\frac{1}{-x}=\frac{1.5-1}{R}\)

or \(, \frac{1.5}{x}+\frac{1}{x}=\frac{0.5}{R}\) or \(\frac{2.5}{x}\)

\(=\frac{0.5}{R}\) or \(x=5 R\)

Distance \(P O=5 R\)