In the dehydrohalogenation of ethyl chloride the following change occurs

${\mathrm{sp}}^2 \mathrm{carbon} \mathrm{converts} \mathrm{to} {\mathrm{sp}}^3 \mathrm{carbon}$

${\mathrm{sp}}^2 \mathrm{carbon} \mathrm{converts} \mathrm{to} \mathrm{sp} \mathrm{carbon}$

${\mathrm{sp}}^3 \mathrm{carbon} \mathrm{converts} \mathrm{to} \mathrm{sp} \mathrm{carbon}$

${\mathrm{sp}}^3\mathrm{carbon} \mathrm{converts} \mathrm{to} {\mathrm{sp}}^2 \mathrm{carbon}$