The paper deals with the cohomological invariants of smooth and connected linear algebraic groups over an arbitrary field. More precisely, we study degree $2$ coefficients $\mathbb{Q}/\mathbb{Z}(1)$, that is taking values in Brauer group. Our main tool \'etale cohomology sheaves on simplicial schemes. We get a description these for \emph{every} groups, particular non reductive imperfect