Answer:
1) NH3->Product
2)  NH4->Reactant
Explanation:
Reactants are the substances in with you start the chemical reaction with (before the arrow)
Products are the result (after the arrow)
 
        
             
        
        
        
Answer:
c. If the double helix were unwound, each nucleotide along the two parent strands would form a hydrogen bond with its complementary nucleotide.
Explanation:
According to the Watson-Crick model, two DNA strands are held together by complementary base pairing wherein each nucleotide of one DNA strand forms hydrogen bonds with its complementary nucleotide present in the other strand. During DNA replication, two DNA strands are separated by the action of helicases enzymes. 
The separated DNA strands serve as a template for DNA replication. Here, each nucleotide of the template DNA strand binds to its complementary nucleotide by hydrogen bonds. For example, adenine of the template strand forms two hydrogen bonds with thymine while guanine forms three hydrogen bonds with cytosine.
 
        
                    
             
        
        
        
A point defined with reference to another position, either fixed or moving; the coordinates of such a point are usually bearing, true or relative, and distance from an identified reference point.