this is based on synergic effect, according to which bond length of CO in metal complex is somewhat larger than the bond length in carbon monoxide.
so ans will be a.
if the bond length of CO bond in carbon monoxide is 1.128 A, then the CO bond length in Fe(CO)5 is :
(a)1.15 A (b)1.128 A
(c)1.72 A (d)1.118 A
this is based on synergic effect, according to which bond length of CO in metal complex is somewhat larger than the bond length in carbon monoxide.
so ans will be a.
But why couldn't it be d) ?? Sorry I haven't read INorganic till now! I meant synergic effect and all that!