Answer:
Pure elements:
Hydrogen(H)
Nitrogen(N)
Magnesium (Mg)
Pure Compounds:
Oxygen gas(O2)  
Water (H2O)  
Ammonia (NH3)
Explanation:
Hope it helps.Please mark me brainliest.^-^
 
        
             
        
        
        
Answer:
Depends on what are you refering to
Explanation:
So depending on what you are looking for (your question is quite vauge)
there are 5 atoms of the comopound (K2CO3)
within that compound, there are 2 atoms of Potassium and 1 atom of Carbonate. Within Carbonate there are 4 atoms (1 carbon and 3 oxygens)
so answers may be
5, 15, or 25.
I hope this helps.
 
        
             
        
        
        
Answer:
The mass of reactants and products are equal hence the reaction obeys law of conservation of mass
Explanation:
The law of mass conservation states that for a closed system to all transfer of mass, the mass of system must remain constant over time. This means for a chemical reaction, the mass of reactants must equal the mass of products.
if 2.796g of Zn reacts with 2.414g of sulphur to produce 4.169g of ZnS ad 1.041g of unreacted sulphur, then it means that accorfing to the law of mass conservation, the mass of reactants (zinc and sulphur), must be equal to mass of products (zinc sulfide and unreacted sulphur)
Mass of reactants = 2.796g + 2.414g =5.21g
Mass of products = 4.169g + 1.041g=5.21g
 
        
             
        
        
        
I believe it is C, but I can't guarantee it.