A potentiometer circuit is set up as shown. The potential gradient across the potentiometer wire, is `k` volt/cm and the ammeter, present in the circuit, reads `1.0` A when two way key is switched off. The balance points, when the key between the terminals (i) 1 and 2 (ii) 1 and 3, is plugged in, are found to be at lengths `l_1 cm and l_2 cm`, respectively. The magnitudes of the resistors `R and X` in ohm, are then, respectively equal to
Options:
(a) `k(l_1-l_2) and kl_2`
(b) `kl_1 and k(l_2-l_1)`
(c) `k(l_2-l_1]) and kl_2`
(d) `kl_1 and kl_2`