$\Lambda_{ m }^{\infty}\left( BaSO _{4}\right)=\lambda_{ m }^{\infty}\left( Ba ^{2+}\right)+\lambda_{ m }^{\infty}\left( SO _{4}^{2-}\right)$

$\Lambda_{ m }^{\infty}\left( BaSO _{4}\right)=\Lambda_{ m }^{\infty}\left( BaCl _{2}\right)+\Lambda_{ m }^{\infty}\left( H _{2} SO _{4}\right)-2\Lambda_{ m }^{\infty}\left( HCl\right)$

$=280+860-2(426)$

$=288 \,Scm ^{2} mol ^{-1}$