a. when is an ion highly polarising ? Which alkali metal ion has the highest polarising power ?
b. What makes lithium to show properties uncommon to the rest of the alkali metals ?

Explanation

a. A cation highly polarising if its (charge/redius) ratio is high. `Li^(o+)` ion having the smallest size will have the maximum (charge/redius) radio or polarising power.
b. Lithium show properties uncommon to the rest of alkali metals due to:
i. Small size of Li atom and `Li^(o+)` ion.
ii. High (charge/radius) ration of `Li^(o+)` ion.