1.

What are chemical twins ? Give examples.

Answer»

Solution :(1) A pair of elements having similar properties due to similar atomic RADII are called chemical TWINS and they are d-block elements of 5TH and 6TH period or 4d-series and 5d-series respectively.
(2) They are Zr and Hf, Nb and Ta, Mo and W, Tc and Re.
(3) This effect arises due to lanthanoid contraction.
Twin elements :
`|{:("Zr (145 pm)","Nb (134 pm)","Mo (129 pm)","Tc (114 pm)"),("Hf (144 pm)","Ta (134 pm)","W (130 pm)","Re (114 pm)"):}|`


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