The variable resistance is called
A.Resistor
B.Rheostat
C.Open switch
D.Closed switch

Hint: If the resistance of the resistor can be altered or varied for our convenience it is called a variable resistor. It is the most significant component found in the electronic circuits or devices which control the tone, bass as well as volume. This is possible because of the fact that the resistance can be connected with the other components to form filters of the desired levels.

Complete answer:
When the variable resistors are used as a potential divider with three terminals it is called a potentiometer. If the same is used with two terminals it is called a rheostat.
Therefore from the given option, the correct answer is a rheostat.

The correct option is B.

Additional Information:
Rheostat has two terminals of which one connection is made at one end of the resistive element and the other end is made at the wiper of the variable resistor. In the earlier days rheostat was used as the power control device in series with a load such as light bulbs. These are not used nowadays as they are insufficient methods.

Note:
The variable resistor is a resistor whose resistance value can be adjusted. They can be operated either mechanically in the case of a potentiometer or rheostat or electronically in the case of a potentiometer. The other types of variable resistors are potentiometer and digital resistors. The potentiometer is most commonly used. They are used as the potential divider. Indigital variable resistors the change in resistance is performed by mechanical movement by means of the electric signal.