phy-electricity

Because the metal sphere is positively charged, it has a POSTIVE POTENTIAL with respect to earth, which is at zero potential.

Electrons has the property that they will go to places of high potential (this is in contrast to positive charges that will go to places of low potential). As such, electrons from earth will flow to the metal sphere, which is at a potential higher than that of earth. Free electrons on the sphere will not go to earth, as the earth is at a potential lower than that of the sphere.

Since the metal sphere is positively charged, it is DEFICIENT in electrons, i.e. total positive charge amount > total negative charge amount.

So when it is earthed, being a big reservior of charges, the electrons of the earth will be ATTRACTED by the sphere due to its positive charge and hence we have:

ELECTRONS WILL MOVE FROM THE EARTH TO THE SPHERE.