B

Bragg's law relates the angle of diffraction, the wavelength of the incident waves, and the spacing between the crystal planes. The law is given by the equation:
$$n\lambda = 2d\sin\theta$$
where:
- $d$ is the distance between the crystal planes
- $\theta$ is the angle of incidence
- $\lambda$ is the wavelength of the X-rays
- $n$ is an integer representing the order of the reflection.

Rearranging the equation for clarity, we see that:
$$d = \frac{n\lambda}{2\sin\theta}$$
The correct form that matches the given options is $n\sin\theta = 2\lambda d$, which is represented in Option B.
Therefore, the answer is B.