Which of the following statements about the stereochemistry of substitution at a chiral secondary carbon are correct?

1. A${\mathrm{S}}_{\mathrm{N}}2$ inverts the spatial arrangement at the reacting carbon.
2. BInversion of configuration always changes the R/S label.
3. C${\mathrm{S}}_{\mathrm{N}}1$ of an optically pure halide gives mostly a racemic product.
4. D$\mathrm{SOCl}{}_2$ without any base converts a chiral secondary alcohol into the chloride with retention (${\mathrm{S}}_{\mathrm{N}}\mathrm{i}$).