If four identical resistors, of resistance 8 ohm, are first connected in series so as to give an effective resistance $R_s$, and then connected in parallel so as to give an effective resistance $R_p$, then the ratio $R_s/R_p$ is

When resistors are connected in series, the effective resistance $R_s$ is the sum of individual resistances. So, $R_s = 8 + 8 + 8 + 8 = 32 ext{ ohm}$. When resistors are connected in parallel, the reciprocal of the effective resistance $R_p$ is the sum of reciprocals of individual resistances. So, rac{1}{R_p} = rac{1}{8} + rac{1}{8} + rac{1}{8} + rac{1}{8} = rac{4}{8} = rac{1}{2}. Therefore, $R_p = 2 ext{ ohm}$. Hence, the ratio rac{R_s}{R_p} = rac{32}{2} = 16.