Assertion :If the distance between parallel plates of a capacitor is halved and dielectric constant is made three times, then the capacitance becomes 6 times.
Reason : Capacity of the capacitor depends upon the nature of the material between the plates.

$$\begin{gathered} \mathrm{C}=\frac{{\mathrm{\epsilon }}_0\mathrm{kA}}{\mathrm{d}}\Rightarrow \mathrm{C} \mathrm{\alpha } \frac{\mathrm{k}}{\mathrm{d}} \\ \therefore \frac{{\mathrm{C}}_1}{{\mathrm{C}}_2}=\frac{{\mathrm{k}}_1}{{\mathrm{d}}_1}\times \frac{{\mathrm{d}}_1}{{\mathrm{k}}_2}=\frac{\mathrm{k}}{\mathrm{d}}\times \frac{\mathrm{d}/2}{3\mathrm{k}}=\frac{1}{6} \\ {\mathrm{C}}_2=6{\mathrm{C}}_1 \\ \mathrm{Again} \mathrm{for} \mathrm{capacity} \mathrm{of} \mathrm{a} \mathrm{capacitor}, \\ \mathrm{C}=\frac{{\mathrm{k\epsilon }}_0\mathrm{A}}{\mathrm{d}} \end{gathered}$$

So, capacity of a capacitor depends upon the medium between two plates of capacitor.
Therefore, both A and R are true but R isnot the correct explanation of A.