Question

explain why the value of g is zero at the centre of the earth

Answer 1

Because at that point the mass of the earth is equally distributed in all directions.

Answer 2

HEY DEAR...
YOUR ANSWER⬇
At the surface of the earth, there is a gravitational force that pulls us down but in the centre of the earth there is no gravitational force that pulls us down any further. Hence the value of g is 0 in the centre.
I HOPE YOU FIND IT HELPFUL.
#LAKSHMI..... :-)