A solenoid of inductance L and resistance R has a soft iron core . It is connected to a battery of E.M.F M as shown in the figure and allowed to attain its steady state.

At an instant , the iron core is suddenly pulled out and because of it. inductance decreases to `L/3`.
The work done by an external agent in pulling out the iron core is

Options

A. `(LE^2)/(R^2)`
B. `(2LE^2)/(R^2)`
C. `(LE^2)/(2R^2)`
D. `(LE^2)/(4R^2)`

Answer

A