A dimer, $Q$, is solid and stable, but in solution it establishes a dynamic equilibrium. $Q(\text{aq}) \rightleftharpoons 2R(\text{aq})$ The starting concentration of a $Q$ solution is $0.50\,\text{mol dm}^{-3}$. Once equilibrium is reached, $[Q(\text{aq})]$ decreases to $0.25\,\text{mol dm}^{-3}$. The variation in $[Q(\text{aq})]$ and $[R(\text{aq})]$ with time is shown on graphs until equilibrium is attained. $K_c$ is then worked out. Which graph and $K_c$ value are correct?