Final answer:
Electrons are the mobile charge carriers that can move onto or off a metallic object when charged objects are brought near, a process known as charging by induction.
Step-by-step explanation:
When charged objects are brought near the sphere, electrons can move onto or out of the metal leaves through the stem. In the process of charging by induction, a positively charged glass rod, for instance, can be brought near a neutral metal sphere, which will attract electrons within the sphere towards itself, leaving the other side of the sphere positively charged.
If the spheres are then separated while the rod is still in proximity, they will retain these induced charges after the rod is removed, without direct contact. This demonstrates the principle that electric charge is conserved and cannot be created or destroyed, but can be separated and redistributed, especially within conducting materials.