When I asked my teacher that what is the acceleration at the centre of earth, he replied that it is 0 as when we move inside the earth, the effective mass decreases i.e. the mass that exerts gravitational force on us decreases and hence at the centre of the acceleration due to gravity is zero.
However when we reach at the centre of earth the radius is also zero hence from the formula - GM/r^2 Where M is mass of earth and r is it's radius, by putting 0 in place of M and r , we get value of acceleration due to gravity = 0/0 which is an undefined quantity.
Even if my teacher was wrong, on Google, the answer for value of acceleration due to gravity is zero and the radius of earth at its centre is also zero so by the formula:- GM/r^2 putting 0 in place of r, we get GM/0 So we get GM/0=0 But GM/0 is again an undefined quantity.
I want ask how is acceleration due to gravity 0 when it is not permitted by the formula as the formula should also be satisfied in every case.