9. In how many of the following species, there is \( \pi \)-character between metal and atom(s) of ligand(s) \( \left[ Cr ( CO )_{6}\right],\left[ Cr \left( PH _{3}\right)_{3}( CO )_{3}\right],\left[ Mo \left( PF _{3}\right)_{3}( CO )_{3}\right],\left[ Fe ( CO )_{4}\right]^{2-},\left[ Co _{2}( CO )_{8}\right],\left[ Fe _{2}( CO )_{9}\right],\left[ Sc \left( H _{2} O \right)_{6}\right)^{3+} \) \( \left[ Ag \left( NH _{3}\right)_{2}\right] Cl ,\left[ Ti ( CO )_{6}\right]^{2-} \)
