Let * be a binary operation on the set Q of rational numbers as follows (i) a * b = a − b (ii) a * b = a2 + b2 (iii) a * b = a + ab (iv) a * b = (a − b)2 (v)a * b = ab/4 (vi) a * b = ab2 Find which of the binary operations are commutative and which are associative.

Let * be a binary operation on the set Q of rational numbers as follows :
(i) a * b = a − b (ii) a * b = a² + b²
(iii) a * b = a + ab (iv) a * b = (a − b)²
 (v)a * b = ab/4  (vi) a * b = ab²
Find which of the binary operations are commutative and which are associative.