(a) 1 only (b) 3 only (c) 1 and 2 (d) 2 and 3

What is a meso form?
Meso form is optically inactive because of the presence of plane of symmetry.In meso form we have two asymmetric
carbon atoms with a plane of Symmetry .
If we put a plane between them and see the reflection of two halves , they are exactly Superimposable miorror   images.Due to this Symmetry element , molecule becomes optically inactive.
In the given question search for plane of Symmetry between chiral centres.
1. and 2 . are completely ruled out. Check for option 3 .