How many electrons are there in $1 \ C$ of charge?

Among the following,the charge that does not exist on any type of charged body is

In Millikan's oil drop experiment, which of the following charges can be present on the oil drop?

The statement that electric charge is an integral multiple of the electronic charge $e$ was experimentally proven by whom?

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:

Consider a neutral conducting sphere. $A$ positive point charge is placed outside the sphere. The net charge on the sphere is then,