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(A) The formula for the internal resistance $(r)$ of a cell using a potentiometer is given by:$r = R \left( \frac{l_1}{l_2} - 1 \right)$where $l_1$ is

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$22.1$

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(A) The formula for the internal resistance $(r)$ of a cell using a potentiometer is given by:$r = R \left( \frac{l_1}{l_2} - 1 ight)$where $l_1$ is the balancing length when the key is open (measuring $EMF$ $E$) and $l_2$ is the balancing length when the key is closed (measuring terminal voltage $V$).Given:$l_1 = 70.0 \, cm$$l_2 = 60.0 \, cm$$R = 132.40 \, \Omega$Substituting the values into the formula:$r = 132.40 \left( \frac{70.0}{60.0} - 1 ight)$$r = 132.40 \left( \frac{70.0 - 60.0}{60.0} ight)$$r = 132.40 \left( \frac{10.0}{60.0} ight)$$r = 132.40 	imes \frac{1}{6}$$r = 22.066 \, \Omega \approx 22.1 \, \Omega$Thus,the correct option is $A$.

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