A small angled prism of refractive index 1.4 is combined with another small angled prism of refractive index 1.6 to produce dispertion without deviation. If the angle of first prism is $6^{\circ}$ , the angle of the second prism is

Question

$\begin {array} {1 1} (1)\;8^{\circ} & \quad (2)\;6^{\circ} \\ (3)\;4^{\circ} & \quad (4)\;2^{\circ} \end {array}$