LiCoO2 crystallises in a rhombohedral structure. Let at initial 100 atoms are present of both
Li and
Co and after
50%Li is extracted only 50 atoms of
Li is remaining. But total charge on the crystal is converted so cobalt have to increase its oxidation state. So,
100Li+100Co=400 50Li+100Co*=400 100Co⋆=350 Co*=3.5 So, after extraction of
50%Li atom new oxidation state of Co to
3.5.
Change in oxidation state = final oxidation state - initial oxidation state
=3.5−3 Change in average oxidation state of
Co=0.5 of of change in average oxidation state of
Co=×100=16.66% (increases)
Hence, the correct option is (b).