What is electrostatic induction?

There are two metallic spheres of same radii,but one is solid and the other is hollow. Then:

$A$ positively charged glass rod is brought near an uncharged metal sphere,which is mounted on an insulated stand. If the glass rod is removed,what is the net charge on the metal sphere?

$A$ $1$ paisa coin is made up of an $Al-Mg$ alloy and weighs $0.75\, g$. It has a square shape and its diagonal measures $17\, mm$. It is electrically neutral and contains equal amounts of positive and negative charges. Calculate the total amount of positive or negative charge in the coin.

When a piece of polythene is rubbed with wool,a negative charge of $4 \times 10^{-7} \ C$ is developed on the polythene. The number of electrons transferred from wool to polythene is $\left[e = 1.6 \times 10^{-19} \ C\right]$.

If a body contains $10^{24}$ electrons and $10^{26}$ protons,the total amount of charge on the body is . . . . . . $C$.