A ray reflected successively from two plane mirrors inclined at a certain angle undergoes a deviation of 300°. The number of observable images is:

A) 60
B) 12
C) 11
D) 5

When a ray of light is reflected successively from two plane mirrors, the total deviation it undergoes is twice the angle between the mirrors. This is because each reflection changes the direction of the ray by twice the angle of incidence.

Let the angle between the two mirrors be θ. The total deviation is given as 300 degrees, which means 2θ = 300 degrees.

So, θ = 300 degrees / 2 = 150 degrees.

Now, to find the number of observable images, we can use the formula:

Number of observable images = 360 degrees / θ

Number of observable images = 360 degrees / 150 degrees

Number of observable images = 12/5

Number of observable images ≈ 2.4

Since the number of observable images must be a whole number, we can round down to the nearest whole number. So, the number of observable images is 2.

However, we also need to consider the original object itself. So, the total number of observable objects, including the original object, is 2 + 1 = 3.

Therefore, the correct answer is not one of the options given (A, B, C, or D), as none of them matches the calculated value of 3 observable images.