The potential difference across the terminals of a battery is 10V when there is a current of 3A in the battery from the negative to the positive terminal. When the current is 2A in the reverse direction, the potential difference becomes 15V. The internal resistance of battery is

Question

$\begin {array} {1 1} (A)\;2.5\: \Omega & \quad (B)\;5\: \Omega \\ (C)\;2\: \Omega & \quad (D)\;1\: \Omega \end {array}$