JEE Advanced 2024 Chemistry question on Coordination Compounds

Among $\mathrm{V(CO)_6}$, $\mathrm{Cr(CO)_5}$, $\mathrm{Cu(CO)_3}$, $\mathrm{Mn(CO)_5}$, $\mathrm{Fe(CO)_5}$, $\mathrm{[Co(CO)_3]^{3-}}$, $\mathrm{[Cr(CO)_4]^{4-}}$, and $\mathrm{Ir(CO)_3}$, the total number of species isoelectronic with $\mathrm{Ni(CO)_4}$ is ______. [Given, atomic number: V = 23, Cr = 24, Mn = 25, Fe = 26, Co = 27, Ni = 28, Cu = 29, Ir = 77]