A cell of emf E and internal resistance r gives current of 0.5 A with external resistance of $12 \Omega$ and a current of 0.25 A with an external resistance $25 \Omega$. What is the value of internal resistance?

$5 \Omega$ $1 \Omega$ $7 \Omega$ $3 \Omega$

$1 \Omega$

The correct answer is Option (2) → $1 \Omega$