What is the acceleration of free fall?

The value of acceleration due to gravity

Consider Earth to be a homogeneous sphere. Scientist $A$ goes deep down in a mine and scientist $B$ goes high up in a balloon. The acceleration due to gravity as measured by:

State whether the following statement is True or False:
The value of $g$ is zero at the centre of the earth.

$A$ stone is dropped from a cliff. Its speed after it has fallen $100 \,m$ is: (in $, m s^{-1}$)

$A$ coin and a piece of paper are dropped simultaneously from the same height. Which of the two will touch the ground first? What will happen if they are dropped in a vacuum? Give reasons for your answer.