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 :

Question

( A ) $4 \Omega$
( B ) $1 \Omega$
( C ) $2 \Omega$
( D ) $0.5 \Omega$