Statement I : Gravitational potential is zero inside a shell
Statement II: Gravitational potential is equal to the work done in bringing a unit mass from infinity to a point inside gravitational field. 

Both S I and S II  are correct and S II is correct explanation of S I

Statement I is correct but Statement II is wrong

Both S I and S II are correct but S II is not correct explanation of S I 

Statement I is wrong but Statement II is correct