The rate of the reaction $\mathrm{Ni}(\mathrm{CO})_{4}+\mathrm{PPh}_{3} \xrightarrow{\Delta}\left[\mathrm{Ni}(\mathrm{CO})_{3}\left(\mathrm{PPh}_{3}\right)\right]+\mathrm{CO}$ depends on
(a)Concentration of both the reactants
(b)Concentration of $\mathrm{Ni}(\mathrm{CO})_{4}$ only