Let the mass and radius of the earth be M and R respectively.
Acceleration due to gravity, g = GM/R^2
When the radius, R’ = R-R/100 = 99R/100 = 0.99R
So, the acceleration due to gravity, g’ = GM/(0.99R)^2
or, g’ = 1.02GM/R^2
Now, the change in acceleration due to gravity,
=g’ – g
=(1.02-1)GM/R^2
= (0.02)GM/R^2
Thus, the acceleration due to gravity increases by 2%.