Why are periscopes used by soldiers sitting in the bunkers ?

Why vinegar is used in pickling?

Why lipase are used in detergents?

Why is choke coil needed in the use of fluorescent tubes with ac mains? Why can we not use an ordinary resistor instead of the choke coil?

Give reason for the following : Why are copper and aluminium wires used as connecting wires ?

Why is photodiode used in reverse bias ?

Why are manure and fertilizers used in fields?

Why are brake pads used in car braking systems ?

Why dry ether is to be used as a solvent for Grignard reagent ?