For Beidellite & Nontronite isomorphous substitution occur in

Solution(By Examveda Team)

For Beidellite & Nontronite isomorphous substitution occur in Tetrahedra.
Beidellite is a mineral that is a common constituent of certain clay and consists of basic aluminosilicate with exchangeable calcium, sodium, or other cation, whereas Nontronite is the iron-rich member of clay minerals.
Moreover, isomorphous substitution is the production of net native charge in clays, and this charge must be balanced by positively charged ions from the solution and helps in the retention of plant nutrients.