Answer:
5.21
Explanation: You can only have 3 digits, so you would round to the hundredths place 
 
        
             
        
        
        
Answer:
It gives the number of protons in the nucleus of each atom of that element. 
Explanation:
 
        
             
        
        
        
Answer: (C) conservation of matter
Solution: Law of conservation of matter or mass states that' total mass of the reactants should always be equal to the total mass of the product that is the total mass is remained conserved in a chemical reaction.
A balanced chemical equation always follow this law.
For example:

Mass of hydrogen = 1 g/mol
Mass of Oxygen = 16 g/mol
Total mass on the reactants = 2(2×1)+(2×16)= 36g/mol
Total mass on the product side = 2[(2×1) +16] = 36 g/mol
As, 
Mass on reactant side = Mass on the product side
Therefore, a balanced chemical reaction follows Law of Conservation of mass.
 
        
                    
             
        
        
        
.035 gallons equals 0.1324894 L