$A$ body can be negatively charged by which of the following methods?

Five balls numbered $1$ to $5$ are suspended using separate threads. Pairs $(1, 2)$,$(2, 4)$,and $(4, 1)$ show electrostatic attraction,while pairs $(2, 3)$ and $(4, 5)$ show repulsion. Therefore,ball $1$ must be:

The charge on $500\,cc$ of water due to protons will be

Number of electrons in one coulomb of charge will be

$(a)$ $A$ 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?

What is called quantization of electric charge? Write the $SI$ unit of electric charge.