Answer:
A-  1 hydrogen, 1 oxygen, 1 chlorine
B-  2 Nitrogen,  4 hydrogen
C-  2 sodium, 2 oxygen 
the last one i dont understand because im in middle school and i havent learned that... :/
Explanation:
 
        
             
        
        
        
To help, I drew a diagram. This represents an ionic bond between Na and Cl. Na is giving his single electron to Cl, which is indicated by the arrow, to make Cl full with 8 electrons.
 
        
        
        
Answer:
A
Explanation:
Lanthanides share the following common properties: Silvery-white metals that tarnish when exposed to air, forming their oxides. Relatively soft metals. Hardness increases somewhat with higher atomic number.
 
        
                    
             
        
        
        
Answer: P2O5 is the empirical formula.
Explanation: When given percentages you can assume that many grams of each atom are in the compound. Then you divide grams by the molar mass of each element, giving you moles. Once you have moles, divide by the smaller molar amount, which should give you 1 mol of Phosphorus and 2.5 mol of Oxygen. Then multiply by 2 in order for both moles to be a whole number. This gets you 2 and 5.