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. 
Let me know if you need further info. 
            - Dotz 
        
                    
             
        
        
        
A. The substance dissolved. Just because a substance dissolved in a solvent doesn’t mean that a chemical action occurred. For example, if you put sugar in water as stir, it will dissolve, but the chemical make up of the sugar and the water don’t change. A chemical reaction can be indicated by a drastic change in color or temperature or if a substance precipitate. 
Hope this helped :)
        
                    
             
        
        
        
statement c would be correct I think.
        
                    
             
        
        
        
Answer:
It is called Ionization Energy.