At what angle should two mirrors be placed so that the left and right of the image in an ordinary mirror stay unchanged?

Think it through first, then pick an option.

a 30°
b 45°
c 60°
d 90°

Answer and explanation

Correct answer: d 90°

When two mirrors at 90° are used as one mirror, the image of one is reflected again in the other and set right, so left and right are not interchanged.

Why the other options are wrong

a 30°: This is not the answer: When two mirrors at 90° are used as one mirror, the image of one is reflected again in the other and set right, so left and right are not interchanged.
b 45°: This is not the answer: When two mirrors at 90° are used as one mirror, the image of one is reflected again in the other and set right, so left and right are not interchanged.
c 60°: This is not the answer: When two mirrors at 90° are used as one mirror, the image of one is reflected again in the other and set right, so left and right are not interchanged.