A first row transition metal ( $M$ ) does not liberate $H_2$ gas from dilute HCl .1 mol of aqueous solution of $\mathrm{MSO}_4$ is treated with excess of aqueous KCN and then $\mathrm{H}_2 \mathrm{~S}(\mathrm{~g})$ is passed through the solution. The amount of MS (metal sulphide) formed from the above reaction is $\_\_\_\_$ mol.