Which of the following changes will increase the emf of the cell :
$\mathrm{Co}\left(\mathrm{s}\right)\left|{\mathrm{CoCl}}_2\left({\mathrm{M}}_1\right)\right|\left|\mathrm{HCl}\left({\mathrm{M}}_2\right)\right|\mathrm{Pt}\left({\mathrm{H}}_2,\mathrm{g}\right)$

Cell reaction :

${\mathrm{Co}}_{\left(\mathrm{s}\right)}+2{\mathrm{H}}_{\left({\mathrm{M}}_2\right)}^{+}\to {\mathrm{Co}}_{\left({\mathrm{M}}_1\right)}^{+2}+{{\mathrm{H}}_2}_{\left(\mathrm{g}\right)}$

From Nernst equation

${\mathrm{E}}_{\mathrm{cell}}={\mathrm{E}}_{\mathrm{cell}}^0-\frac{0.0591}{2}\log \frac{\left[{\mathrm{Co}}^{+2}\right]\left[{\mathrm{P}}_{{\mathrm{H}}_2}\right]}{{\left[{\mathrm{H}}^{+}\right]}^2}$

on dilution [Co⁺²] decreases, E_cell decreases.

[H⁺] increases, E_cell increases.

Partial pressure of H₂ increases,E_cell decreases.