c
\(f_1=500 \times 10^3 \,Hz\)

\(L^{\prime} \rightarrow 2 L, \quad C^{\prime} \rightarrow \frac{1}{8} C\)

\(f=\frac{1}{2 \pi \sqrt{L C}} \Rightarrow f \propto \frac{1}{\sqrt{C L}}\)

\(\frac{f_1}{f_2}=\frac{\sqrt{L_2 C_2}}{\sqrt{L_1 C_1}}=\sqrt{\frac{(2 L)\left(\frac{1}{8} C\right)}{L C}}\)

\(\frac{f_1}{f_2}=\frac{1}{2} \Rightarrow f_2=1000 \,kHz\)