All salts are soluble in water and give strong acid and weak base $ SrCl_2 + 2H_2O \longrightarrow Sr (OH)_2 + 2HCl $ $ BaCl_2 + 2H_2 O \longrightarrow Ba(OH)_2 + 2 HCl $ $ MgCl_2 + 2H_2O \longrightarrow Mg(OH)_2 + 2HCl $ $CaCl_2 + 2H_2 O \longrightarrow Ca(OH)_2 + 2HCl $ The basic nature of alkaline earth metals is generally increases from Be to Ra. Thus, the order of basic nature of these hydroxides is $Mg(OH)_2 < Ca(OH)_2 < Sr(OH)_2 < Ba(OH)_2$ Hence, pH is highest for $BaCl_2$. (As pH increases with basic nature)