The ${\left(\frac{\partial \mathrm{E}}{\partial \mathrm{T}}\right)}_{\mathrm{P}}$ of different types of half cells are as follows :

A	B	C	D
$1\times {10}^{-4}$	$2\times {10}^{-4}$	$0.1\times {10}^{-4}$	$0.2\times {10}^{-4}$

(Where $E$ is the electromotive force)

Which of the above half cells would be preferred to be used as reference electrode?

A cell with less variation in EMF with temperature is preferred as reference electrode because it can be used for wider range of temperature without much derivation from standard value so a cell with less ${\left(\frac{\partial \mathrm{E}}{\partial \mathrm{T}}\right)}_{\mathrm{P}}$ is preferred.