C is the correct answer (CaF2) (sorry dont have subscript)
Explanation: synthesis reaction forms a compound and calcium reacting with fluorine produces Calcium Fluoride (CaF2) chemical name
        
                    
             
        
        
        
1) is sulfuric acid
2)is nitrous acid
3)is hydrochlorous acid
4)is hydrobromous acid
5)is hydrophosphoric acid
6)is fluoric acid
7)is sulfuric acid
8)is chlorous acid
9)is nitric acid
10)is iodic acid
11)is acetous acid
12)is chlorous acid.
        
             
        
        
        
H ( hydrogen ) is the answer I believe.
        
                    
             
        
        
        
B) land cools off much faster than water (creating a air region of high density  above land and lower density above sea)
 
        
             
        
        
        
X is dependent Y is independent.... number of students is Y flavor is X