Answer:
Chemical symbol
This is used to identify an element without having to write the full name and as such is a designation for the element. It is used in chemical reactions and is usually either one or two letters. Some symbols are, Iron - Fe, Hydrogen - H and Oxygen - O. 
Valency 
This refers to the capacity of an element to combine with another to form a compound. It is measured by the number of electrons that an atom of an element gains, looses or shares when a chemical reaction involving it takes place. 
 
        
             
        
        
        
Answer:

Explanation:
1. Write the skeleton equation for the half-reaction
NO₃⁻ ⟶ N₂O
2. Balance all atoms other than H and O
2NO₃⁻ ⟶ N₂O
3. Balance O by adding H₂O molecules to the deficient side.
2NO₃⁻ ⟶ N₂O + 5H₂O
4. Balance H by adding H⁺ ions to the deficient side.
2NO₃⁻ + 10H⁺ ⟶ N₂O + 5H₂O
5. Balance charge by adding electrons to the deficient side.
2NO₃⁻ + 10H⁺ + 8e⁻ ⟶ N₂O + 5H₂O
The amount of charge required to reduce 2 mol of NO₃⁻ is 8 F

 
        
                    
             
        
        
        
Answer:People can drown or call or slip in
Explanation:
 
        
                    
             
        
        
        
Answer:
<h2>A. Mercury's orbit is shorter than Earth</h2>