**Answer:**

When two plane mirrors are kept parallel to each other, they form multiple images of an object placed between them. The number of images formed depends on the angle between the mirrors and the position of the object.

Given, distance between the mirrors = 600 cm

To find the number of images formed, we can use the formula:

Number of images = (360°/angle between the mirrors) - 1

where angle between the mirrors = 360°/n where n is an integer representing the number of images formed.

Now, let's calculate the angle between the mirrors:

angle between mirrors = 360°/n = 360°/2 = 180°

Therefore, the angle between the mirrors is 180°.

Substituting this value in the formula, we get:

Number of images = (360°/180°) - 1 = 2 - 1 = 1

Thus, we can conclude that when two plane mirrors are kept 600 cm apart, only one image of an object placed between them is formed.

However, if the object is placed at a certain distance from the mirrors, multiple images can be formed due to the reflection of light rays. The number of images formed in such cases can be calculated using the same formula mentioned above.

For example, if the object is placed at a distance of 200 cm from one of the mirrors, three images will be formed. If it is placed at a distance of 150 cm from one of the mirrors, five images will be formed.

In the given options, option B (5) is the correct answer if the object is placed at a distance of 200 cm from one of the mirrors. If the object is placed at a different distance, the number of images formed will be different.