Q.You are given four bulbs of 25 W, 40 W, 60 W and 100 W of power, all operating at 230 V. Which of them has the lowest resistance? (A) 25 W (B) 40 W (C) 60 W (D) 100 W

Ohm's law, discovered experimentally by Georg Simon Ohm in 1828, states that the current $I$ through a conductor is directly proportional to the potential difference $V$ applied across it, provided the conductor's physical state (notably its temperature) stays unchanged. Writing $I\propto V$ as $V=IR$ defines the RESISTANCE $R=V/I$ of the conductor, measured in ohms ($\Omega$); the reciprocal of resistance is called conductance, $C=1/R$, measured in siemens.

Microscopically, Ohm's law arises from the free-electron drift picture: an applied field $E$ accelerates each electron between successive random collisions with the lattice's ion cores, building up an average drift speed $V_d=eE\tau/m$ (where $\tau$ is the mean time between collisions); this leads to $E=\rho J$, where $\rho=m/(ne^2\tau)$ is the material's resistivity -- a quantity built purely from constants of the material ($m$, $n$, $e$, $\tau$) and therefore itself INDEPENDENT of the applied field. It is precisely this field-independence of $\rho$ that makes $J$ (and hence $I$) scale in direct proportion to $E$ (and hence $V$), which is exactly what Ohm's law states.