I have a confusion, They say that electric field inside a conductor is always zero, If it is then come we gwt an expression for the field inside a charged sphere ?Shouldnt it be zero as well

u r talking about a charged sphere where the charge is uniformly distributed throughout its volume and its not a conductor
in case of a conductor all charge resides on the surface
so dV/dr will be 0. . hence E=0
but in charged sphere dV/dr =/= 0 as charge is present throughout the volume

For a detailed explanation of why electric field is zero inside the conductor,read Hc Verma(pg 113 part 2)

U will understand that the electric field inside the conductor is zero since the induced electric field inside cancels the outside electric field.But in case of charged sphere electric field cant be induced inside the sphere because it has either one of charges(ie,+ve and -ve).And hence there will be a net electric field inside the sphere.