The device to convert alternating current into direct current is

A rectifier is a device that converts alternating electric current into direct current. It may be an electron tube (either a vacuum or a gaseous type), vibrator, solid-state device, or mechanical device. Hence option B is correct. A transformer is a device that transfers electric energy from one alternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage. An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. A Condenser is a device for reducing a gas or vapour to a liquid. Condensers are employed in power plants to condense exhaust steam from turbines and in refrigeration plants to condense refrigerant vapours, such as ammonia and fluorinated hydrocarbons.