The natural frequency of an L - C circuit is 125000cycles / s ....

$f = \dfrac{1}{2\pi\sqrt{LC}}$

When a dielectric is introduced the capacitance becomes

${C }^{′} = K C$

$⇒ \dfrac{f{}^{'}}{f} = \sqrt{\dfrac{C }{C{}^{'}}}$

$\dfrac{125000 - 25000}{125000} = \sqrt{\dfrac{C }{KC}}$

$\dfrac{100}{125} = \dfrac{1}{K}$

$K = \left(\dfrac{125}{100}\right)2 = 1.56$