Which of the following is used for the estimation of halogens in organic compounds?

Arrange the following carbanions in order of their decreasing stability

(i) ${\mathrm{H}}_3\mathrm{C}-\mathrm{C}\equiv {\mathrm{C}}^{-}$

(ii) $\mathrm{H}-\mathrm{C}\equiv {\mathrm{C}}^{-}$

(iii) ${\mathrm{H}}_3\mathrm{C}-{\mathrm{CH}}_2^{-}$

The configuration of the compound