When the momentum of a proton is changed by an amount $p_{\circ}$, the corresponding change in de- Broglie wavelength is found to be $0.25 \%$. Then, the original momentum of the proton was

Question

$\begin {array} {1 1} (a)\;p_{\circ} & \quad (b)\;100\: p_{\circ} \\ (c)\;400\: p_{\circ} & \quad (d)\;4\: p_{\circ} \end {array}$