0.5 moles of gas $$A$$ and $$x$$ moles of gas $$B$$ exert a pressure of $$200\text{ Pa}$$ in a container of volume $$10\text{ m}^3$$ at $$1000\text{ K}$$. Given $$R$$ is the gas constant in $$\text{J K}^{-1}\text{ mol}^{-1}$$, $$x$$ is

A

$$\frac{2R}{4 + R}$$

B

$$\frac{2R}{4 - R}$$

C

$$\frac{4 - R}{2R}$$

D

$$\frac{4 + R}{2R}$$