Four metal conductors having different shapes:
$1.$ $A$ sphere
$2.$ Cylindrical
$3.$ Pear
$4.$ Lightning conductor
are mounted on insulating stands and charged. The one which is best suited to retain the charges for a longer time is:

What is the charge on an electron?

What type of charges are obtained on silk cloth and glass rod when they are rubbed against each other?

When a piece of polythene is rubbed with wool,a charge of $-2 \times 10^{-7} \ C$ is developed on the polythene. What is the amount of mass transferred to the polythene?

Rubbing a plastic rod with wool gives the plastic rod a negative charge of $8 \times 10^{-7} \ C$. How many electrons have been transferred,and from where to whom?

Two identical conducting balls $A$ and $B$ have positive charges $q_{1}$ and $q_{2}$ respectively,where $q_{1} \neq q_{2}$. The balls are brought together so that they touch each other and then separated to their original positions. The force between them is