Cohomological invariants of algebraic tori

Let G be an algebraic group over a field F. As defined by Serre, a cohomological invariant of G of degree n with values in Q = Z. j/is a functorial-in-K collection of maps of sets TorsG. K/F H-n. K; Q = Z. j/Ffor all field extensions K= F, where TorsG. K/is the set of isomorphism classes of G-torsors over Spec K. We study the group of degree 3 invariants of an algebraic torus with values in Q = Z.2/. In particular, we compute the group H-nr.(3) F(S) Q = Z.2//of unramified cohomology of an algebraic torus S.