Question

why is it necessary to earth metallic appliances​

Answer 1

because if any leakage of current get tranferred to the earth and the user may not get any shock.

So it is
necessary to earth metallic appliances

MARK AS BRAINLIST

Answer 2

here is your answer mate....

to protect the user when if the application's wire's protecting insulting cover removes or broken down it may give shock to the user when touched to the metallic body... but when the earthed wire is joint with the body it does not let current to pass through the user and current passes through the earth Wire and goes into the earth....