One way is by using Cramer-Rao Lower Bound This will also tell you whether it is attained.
Let X1,X2,...,Xn be a random sample from a distribution with p.d.f.,
Obtain minimum variance unbiased estimator of θ and examine whether it is attained?
Using MLE i have found the estimator for θ=2/(x bar)
so can i take x/2 as unbiased estimator of θ. I'm stuck and confused need some help.