A parallel plate capacitor with circular plates of radius 10 cm has...

The displacement current between the capacitor plates is given by:
$I_d = C \dfrac{dV}{dt}$
$I_d = 50 \times 10^{-6} \times 20 = 10^{-3} \text{ A}$

According to the Ampere-Maxwell law, the line integral of the magnetic field around the edge of the plates is equal to $\mu_0$ times the total displacement current enclosed:
$\oint \vec{B} \cdot d\vec{l} = \mu_0 I_d$
$B(2\pi R) = \mu_0 I_d$

Substituting the given values ($R = 10 \text{ cm} = 0.1 \text{ m}$):
$B = \dfrac{\mu_0 I_d}{2\pi R}$
$B = \dfrac{4\pi \times 10^{-7} \times 10^{-3}}{2\pi \times 0.1}$
$B = \dfrac{2 \times 10^{-10}}{0.1} = 2 \times 10^{-9} \text{ T}$

Option 1 is incorrect as a changing electric field induces a magnetic field even in the absence of conduction current.
Option 3 is incorrect as it misses the $2\pi$ factor in the denominator.
Option 4 is incorrect as it divides by the area $\pi R^2$ instead of the circumference $2\pi R$.

Answer: $2 \times 10^{-9} \text{ T}$