To get 9 multiple images the angle between two plane mirrors should be :

Foundation

Physics Foundation

Reflection from plane mirror

Question

50º

90º

60º

36º

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Number of image may be given by
n = $\frac{360 º}{θ}$ or n = $\frac{360 º}{θ} - 1$

i.e. $\frac{360 º}{n + 1} \leq θ \leq \frac{360 º}{n}$
here n = 9
Range of θ will be
36º ≤ θ ≤ 40º
so correct option is θ = 36º