In a potentiometer experiment the balancing with a cell is at length $$240$$ cm. On shunting the cell with a resistance of $$2 \Omega$$ the balancing length becomes $$120$$ cm. The internal resistance of the cell is

A

$$1 \Omega$$

B

$$0.5 \Omega$$

C

$$4 \Omega$$

D

$$2 \Omega$$