CEC of which of clay mineral is highest (120 - 150 cmol/kg)

CEC of Vermiculite is the highest of the given options and it is about 120 - 150 cmol/kg.
CEC (cation exchange capacity) is the measure of its ability to absorb cations from the solution. It has been defined as the number of cations that are available at a given pH for exchange with other cations.
Vermiculite is the name of a group of hydrated laminar minerals (aluminum-iron magnesium silicates) that look like mica. It is a hydrous phyllosilicate mineral that undergoes significant expansion when heated.