Sodium $(S)$-2-bromopropanoate, $\mathrm{CH}{}_3\mathrm{CH}(\mathrm{Br})\mathrm{COO}{}^{-}\mathrm{Na}{}^{+}$, is hydrolysed in dilute aqueous alkali. Assume that the rate-determining step is intramolecular displacement of bromide by the carboxylate oxygen (forming a three-membered alpha-lactone, with inversion), followed by SN2 opening of the lactone by water or hydroxide at the same carbon (another inversion). The net stereochemical result, the CIP descriptor of the lactate product, and the dependence of the rate on $[\mathrm{OH}{}^{-}]$ are

1. Aretention; $(S)$-lactate; rate independent of $[\mathrm{OH}{}^{-}]$
2. Binversion; $(R)$-lactate; rate independent of $[\mathrm{OH}{}^{-}]$
3. Cretention; $(S)$-lactate; rate proportional to $[\mathrm{OH}{}^{-}]$
4. Dinversion; $(R)$-lactate; rate proportional to $[\mathrm{OH}{}^{-}]$