Answer:
A class system is a more smooth system, caste is more of a system that changes consistently. 
Explanation:
"Class system is typically more fluid than the caste system or the other types of stratification and the boundaries between classes are never clear-cut. Caste system is static whereas the class system is dynamic. ... In the caste system, individual mobility from one caste to another is impossible."
 
        
             
        
        
        
First one should be true because neutrons don't carry a charge therefore they won't affect the overall charge of the atom. 
Second one should be positively charged, dense, and contains most of the mass of the atom
        
             
        
        
        
The attached ribosomes make protein 
 
        
                    
             
        
        
        
Five major Arthropod classes
Arachnida. mites, ticks, spiders, scorpions.
Chilopoda. Centipedes.
Crustacea. (crabs, lobsters, shrimp.
Diplopoda. Millipedes.
Hexapoda. Insects.
so your answer will be mollusks