Let \(*\) be binary operation on non-zero rational number \(Q^+\) defined by \(a*b=\frac{ab}{2}\) for all \(a,b\in Q^+\) then identity element is

1 2 0 3

2

for identity element $e$ \(a*e=\frac{ae}{2}=a\) $⇒ae=2a$ so $e=2$