A) Reduce the mass to one fourth
Explanations:
The frequency of spring oscillator is
\(v=\frac{1}{2\pi}\sqrt\frac{k}{m}\)
\(\implies v\propto \sqrt\frac{1}{m}\)
Hence \(\frac {v_1}{v_2}=\sqrt\frac{m_2}{m_1}\)
or \(\frac{m_2}{m_1}=(\frac{v_1}{v_2})^2=(\frac{v}{2v})^2=\frac{1}{4}\)
\(m_2=\frac{m_1}{4}\)