A conducting sphere in an external field.

The electric field in a conductor is always zero. If it were not to be zero, there would be a force on the charges within the conducting sphere which would mean we would no longer be dealing with electrostatics, as when there is a force there is movement. This movement would consequently produce a magnetic field. As we know that we are not dealing with moving charges, the magnitude of the electric field must be zero.

no electric feild line enters inside the conducting material.

According to Gauss's Law for electric field, there is no net charge inside the sphere (and hence no electric field). The electric field (or charge) entering the sphere must be equal to electric field (or charge) leaving the field.

E=0 inside the conductor because all the charges are distributed on the surface of the conducting sphere. The Gaussian surface which lies entirely on the surface of the conducting sphere encloses no charge, so there is no source of electric field. Therefore, no electric field detected or measured inside a conducting sphere.

We know that that the electric field inside a conductor is zero when placed in an external electric field. The electrons in the conducting sphere will redistribute in such a way to create an internal electric field which opposes the existing one such as to make the electric field at all points inside the conductor , zero , no matter the magnitude of external electric field or the charge on the conductor. Note that

As we know that sphere is conducting therefore all charge is at the surface.

If we take a Gaussian surface exactly same size as sphere and apply definition of electric field i.e., electric field is (1/e) times the charge enclosed within the Gaussian surface.

Therefore, as charge enclosed is zero , hence electric field is zero.

Trick question. The field inside a conductor is always zero: the electrons are free to rearrange themselves against the external field :P

Electric field lines cannot penetrate a metal surface, that's how faraday cage works. Check here:

https://en.m.wikipedia.org/wiki/Faraday_cage

Clearly, inside a sphere, the electric field generated is cancelled out from all the sides and the net electric field at the center is $\boxed{zero}$ .

According to Gauss's law, the electric field is proportional to the total charge enclosed in a given region. On a conductor, the charge will distribute over the surface. So there is no charge at the center.Even being put into an electric field, this will only induce charge on the surface but not within the sphere, hence the field inside is still 0.

Since in electrostatics, the electric field inside the perfect conductor is always $0$ , no matter what is present outside or on the surface of the conductor, answer is $0$ .