Among the following compounds, the one which shows highest dipole moment is

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2-Methyl propyl bromide reacts with $$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O}^{-}$$ and gives 'A' whereas on reaction with $$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$$ it gives 'B'. The mechanism followed in these reactions and the products 'A' and 'B' respectively are :

The pair of lanthanides in which both elements have high third - ionization energy is :