$A$ polythene piece rubbed with wool is found to have a negative charge of $3.52 \times 10^{-7} \text{ C}$. What is the number of electrons transferred?

Mention the types of methods of charging a body.

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:

$(a)$ $A$ comb run through one's dry hair attracts small bits of paper. Why? What happens if the hair is wet or if it is a rainy day? (Remember,a paper does not conduct electricity.)
$(b)$ Ordinary rubber is an insulator. But special rubber tyres of aircraft are made slightly conducting. Why is this necessary?
$(c)$ Vehicles carrying inflammable materials usually have metallic ropes touching the ground during motion. Why?
$(d)$ $A$ bird perches on a bare high power line,and nothing happens to the bird. $A$ man standing on the ground touches the same line and gets a fatal shock. Why?

From the following,what charges can be present on oil drops in Millikan's experiment? (Here $e$ is the electronic charge)

$A$ solid of mass $1 \ kg$ has $6 \times 10^{24}$ atoms. If one electron is removed from every one atom of $0.005 \%$ of the atoms,then the charge gained by the solid is