Why electric field inside a hallow shell is zero.

Reason:-

Charge resides only on the surface of conductor so the total charge of hallow shell(shell means closed surface) lies on their surface.Therefore charge inside the hallow shell is zero.

According to Gauss's theorem 

  Integration of E•dA=q(inside)/epsilon

Here total charge inside the hallow shell is zero

So integration of E•dA=0/epsilon=0

        That implies E=0

It is the answer to the question why electric field inside the hallow shell is zero.