NH+4 fixation takes place in

Answer: Option A

Fixation of NH⁺₄ takes place in crystal lattices of different clay minerals like montmorillonite, illite and vermiculite. Illite typically weathers to vermiculite through the release of potassium ions from the interlayer.
Fixation of ammonium ions by clay minerals is an alternate way of building the nitrogen pool in the soil to optimize N crop recovery and minimize losses.