Where should an object is placed in front of a convex lens to get a real image of the size of the object?
At twice the focal length.
Explanation for correct option
Option B,
When the object is at (twice the focal length )
Option B is correct.
Explanation of incorrect options
Option A,
When the object is at (principal focus of the lens)
Option A is incorrect.
Option C,
When the object is at infinity,
Option C is incorrect.
Option D,
When the object is between the optical center of the lens and its principal focus
Option D is incorrect.
Therefore, option B is correct.