An electric bulb is rated '$100\mathrm{W},250\mathrm{V}$‘, The resistance of the bulb is:

Any conductor, even a lightbulb, will block the flow of an electric current; this obstruction is known as electrical resistance and is represented by the letter R. Conductors emit heat when current flows through them because all materials have an electrical resistance.

Given:
Lamp Power P = 100W
Lamp Voltage V = 250V
The power, voltage, and resistance relationship is given if
$R = V^{2}P$
R is tolerant of the lamp.
If you change the power and voltage values ​​in the above equation, you get
$R = {\left(250V\right)}^2/100 W = 62500/100 = 625 \Omega .$
Therefore, the correct answer is option B, or 625 $\Omega$.