The absorption of visible light and hence coloured nature of the transition metal cation is due to the promotion of one or more unpaired - d - electron from a lower to higher level within same d-subshell. Hence higher will be the number of unpaired electron higher will be the absorpion in visible light. The electronic configuration of the given elements is Sc3+(18)=1s22s22p63s23p63d04s0− no unpaired e−. Ti4+(18)=1s22 s22p63s23p63d04s0− no unpaired e−. V3+(20)=1s22s22p63s23p63d24s0 - Two unpaired e−. Zn2+(28)=1s22s22p63s23p63d104s0− no unpaired e−. hence [V(NH3)6]3+ will most likely absorb visible light.