Zn, Cd, and Hg are not regarded as transition elements on the basis of electronic configuration because
1 they do not have electrons in d-subshell
2 their d and s-subshell remain fully filled in ground and higher oxidation states
3 their s-subshell remain incomplete in ground and ionic state
4 their penultimate shell remains completely filled in ground and in higher oxidation state



The answer is the option 4.
The Brainliest Answer!
Transition metals properties comes from their chemistry involves electron from d-orbitals. 
Zn,Cd,Hg chemistry involves only the electron in their s-orbitals hence (4) option is correct
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