Https://superhumanacademy.com/how-to-memorize-polyatomic-ions-chemical-formulas/ 
This is how I memorized the ionic formulae. It is a lot to remember, so it does take some time and studying. But this website helped me learn it fast and in a suuuper unique way. I learned it 3 years ago and could still name quite a bit of them. Hope this helps!!!
        
             
        
        
        
The information given in the question is not enough to determine the acidity of the solution. This is because, acidity can only be found with the equation: pH = -log [H+].
 In order to determine the acidity of the solution, the half titration point value is needed, this will make it possible to determine the value of H30+.  If the half point titration value is known, then Ka will be equivalent to pH and the value will be evaluated using the equation: - log (1.6 * 10^-10).
        
             
        
        
        
 Well you have to mix chemicals which caused a chemical reaction. When you mix salt and ice the freezing point of liquid changes. the ice gets colder
 
        
                    
             
        
        
        
Option C: Sulfur Dioxide is the answer  
Hope this helps