let recall the rate= M/ s, also that brackets, [ ], represent molar (M= mol/ liters).
if we solve the formula for K, we get--> K= rate/ [A] [B]
if we plug in the units of each value we get
K= (M/s)/ (M x M)
we then simply
K= M^-1 s^-1
or
K= mol-1 L-1 s-1
