Which one of the following cyano complexes would exhibit the lowest value of paramagnetic behaviour?
(At. No. Cr = 24, Mn = 25, Fe = 26, Co = 27)

Tertiary alkyl halides are practically inert to substitution by S_N2 mechanism because of

Elimination of bromine from 2-bromobutane results in the formation of-

Alkyl halides react with dialkyl copper reagents to give