2 equal charges are kept at x=a and x=-a. there can be only 1 point where the electric field will be 0? how, can anyone explain?

At the midpoint of the line joining the two equal charges

Explanation:

The midpoint of the line joining the two equal charges has equal distance from each charge. Since the charges are at x = a and x = -a, at the midpoint of the line joining the two equal charges, the magnitude of the electric field experienced as a result of each charge is the same. But these two fields are in opposite direction, hence the net resulting electric field would be equal to zero.

this could be newton#'s law of cooling. the cooling curve is exponential

your answer is, orbit around the nucleus