Answer
$I_B\lt I_C=I_A\lt I_D$
Work Step by Step
case A: The intensity is given as $I=\frac{1}{2}I_{\circ}cos^260^{\circ}$
$I_A=I_{\circ}(0.125)$
casB: The angle $\theta=90^{\circ}$
$I_B=\frac{1}{2}I_{\circ}cos^290^{\circ}=0$
hence $I_B=0$
case C: Now the angle is $\theta=60^{\circ}$
$I_C=\frac{1}{2}I_{\circ}cos^260^{\circ}$
$I_C=I_{\circ}(0.125)$
case D: Now the angle is $\theta=30^{\circ}$
$I_D=\frac{1}{2}I_{\circ}cos^230^{\circ}$
$I_D=(0.375)I_{\circ}$
Thus the order of the increasing amount of intensity is
$I_B\lt I_C=I_A\lt I_D$
