Answer:
Option C. the sharing of electrons between atoms 
Explanation:
Covalent bond is a type of bond in which the reacting element share their valence electrons in order to attain the noble gas configuration. 
 
        
             
        
        
        
  2 Li(s)  +Cl₂→  2 Li⁺ (aq)  + 2Cl⁻ (aq)
The cell potential   of  the reaction above   is +4.40V
<em><u>calculation</u></em>
 Cell  potential  =∈° red - ∈° oxidation
  in  reaction above  Li  is  oxidized from oxidation state 0 to +1 therefore the∈° oxid = -3.04
   Cl  is  reduce   from oxidation  state  0 to -1 therefore  the ∈°red = +1.36 V
cell  potential is therefore = +1.36 v -- 3.04  = + 4.40 V
  
        
             
        
        
        
Acid - base indicators (also known as pH indicators) are substances which change color with pH. They are usually weak acids or bases. you use them if you want to know if a solution is an acid or it it's a base
        
             
        
        
        
Answer:
Ammonia is the richest source of nitrogen on a mass percentage basis because it has 82.35% of nitrogen by mass.
Explanation:
Percentage of element in compound :

(a) Urea, 
Molar mass of urea = 60 g/mol
Atomic mass of nitrogen = 14 g/mol
Number of nitrogen atoms = 2

(b) Ammonium nitrate, 
Molar mass of ammonium nitrate = 80 g/mol
Atomic mass of nitrogen = 14 g/mol
Number of nitrogen atoms = 2

(c) Nitric oxide, NO
Molar mass of nitric oxide  = 30 g/mol
Atomic mass of nitrogen = 14 g/mol
Number of nitrogen atoms = 1

(d) Ammonia, 
Molar mass of ammona = 17 g/mol
Atomic mass of nitrogen = 14 g/mol
Number of nitrogen atoms = 1
Ammonia is the richest source of nitrogen on a mass percentage basis because it has 82.35% of nitrogen by mass.