The simplex CLT

Starting from \operatorname{Cov}(X_j,X_k)=-np_jp_k for j\neq k and \operatorname{Var}(X_k)=np_k(1-p_k), derive the covariance matrix of \sqrt n(\widehat{\boldsymbol{p}}-{\boldsymbol{p}}). Show that multiplication by the all-ones vector gives zero.

This exercise has no worked answer.