Number 3:
Chlorine, Sodium, Sulfate, Magnesium, and Calcium.
Number 4:
The salt Increases/Decreases the density.
Hope this helps you! 
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Explanation:
The dimensions of a standard backpack is 30cm x 30cm x 40cm
The mass of an average student is 70 kg
We know that, the density of gold is 19.3 g/cm³.
Let m be the mass of the backpack. So,

An average student has a mass of 70 kg. If we compare the mass of student and mass of backpack, we find that the backpack is 10 times of the mass of the student.
 
        
             
        
        
        
Answer: most store-bought isnt 
Explanation:
there typically a lot of addivitves
 
        
             
        
        
        
Answer:
Decomposition or cracking
Explanation:
Decomposition reaction is a chemical change in which a single compound is broken down into two or more simpler products. 
   For example; 
                    A     →    B   +  C 
  The driving force of such reaction is the high positive heat of formation of the compound which indicates that they are highly unstable. 
Some stable compounds also decompose when subjected to high temperature and pressure.