Question

at the mid point of the line joining two identical charges
1) both intensity and potential are zero
2)potential is zero but intensity is not zero
3)intensity is zero but potential is not zero
4)both intensity and potential are non-zero

Answer 1

I'm assuming by intensity you are referring to the magnitude of the total force, which lead to 3 being the correct answer as the forces are opposite each other and the potential is not zero for both of the charges. Otherwise the question and associated answers are poorly worded.

Answer 2

I suspect "intensity" means "electric field." If so, field is zero, cancels, but potential is non-zero.