Step 1:

The terminal voltage $\"\"$ is $\"\"$ and current $\"\"$ is $\"\"$ .

When the load is disconnected, the terminal voltage rises to $\"\"$ is $\"\"$ .

Then the internal potential difference $\"\"$ is $\"\"$ .

$\"\"$

Here current is constant, because cell is connected in series.

So $\"\"$

$\"\"$

The internal resistance of the cell is $\"\"$ .

Solution :

The internal resistance of the cell is $\"\"$ .