In Young's double-slit experiment, the distance between adjacent maxima (or minima) is given by:
\[
y = \frac{\lambda L}{d}
\]
where \( \lambda \) is the wavelength, \( L \) is the distance from the slits to the screen, and \( d \) is the distance between the slits.
The distance between the 6th maxima and the 10th minima is the distance between the 6th maxima and the 10th minima. The total distance is:
\[
y = (6 - 10) \cdot \frac{\lambda L}{d} = 4 \cdot \frac{500 \times 10^{-9} \times 1}{0.2 \times 10^{-3}} = 8 \, \text{mm}
\]
Thus, the correct answer is (D).