Instructors may choose to vary the membership of some marginal elements including the group 3 metals; aluminium; and silver and the group 12 metals. The group 3 metals, and aluminium due to its putative reactivity, can alternatively be collocated with the s-and f-block metals in which case the resulting set could be referred to as the active metals. Silver may be excluded from the noble metals due to its higher reactivity and predominately main-group chemistry. It and the group 12 metals plus the p-block metals could be referred to as post-transition metals. The remaining d-block metals become transition metals.