Barium (Ba) has the lowest electronegativity of the choices you have given.
The electronegativity of Calcium (Ca) is 1 The electronegativity of Strontium (Sr) is 0.95 The electronegativity of Magnseium (Mg) is 1.31 (has the highest) The electronegativity of Barium (Ba) is 0.89
Of the list above, you can see that Barium has the lower level of electronegativity (0.89). Therefore, the correct answer is D.
