1.Ans:

Here,

From the information given from table,

 In lens A when the position of image is beyond 2F it forms real, diminished and inverted image. Similarly, in lens B when the position of image is between F and O it forms virtual, magnified and erected image. Hence, lenses A and B are convex lenses.

Thus, lenses A and B can be used in the remedy of long sightedness as they help converge the rays of light on retina form closer objects for formation of their clear image.

2.Ans:

Here, \(\rm OF_{1}\)= \(\rm OF_{2}\) = \(\rm 3cm\)

So, \(\rm O2F_{1}\)= \(\rm O2F_{2}\) = \(\rm 6cm\), This should be the measurement when ray diagram is drawn.

3.Ans:

Here, from the table it is identified that lens C is a concave lens.

Concave lenses always produce virtual, upright, and diminished images, regardless of the object's position.

Hence, nature of image formed by the lens C when object is kept at 2F of it is also virtual, erected and diminished. 

But, comparatively to the given condition, the image will be more diminished when kept at 2F.