Answer:- Oxidation number of Cl does not change as it is -1 on both sides.
Explanations:- oxidation number of Mg on reactant side is 0 as it is in its elemental form(not combined with another element).
Oxidation number  of hydrogen in its compounds is +1, so if H is +1 in HCl the oxidation number of Cl is -1 as the sum has to be zero.
On product side, Mg oxidation number is +2 as the oxidation number of alkaline earth metals in their compounds is +2.
Two Cl are present in magnesium chloride, so if Mg is +2 then Cl is -1. 
Oxidation number of H on product side is 0 as it is present in its elemental for,  ,
 ,
So, it is only chlorine(Cl) whose oxidation number does not change for the given equation.
 
        
             
        
        
        
The number of bacteria is given by:
N(t) = N(o) x 2ⁿ
Where N(t) is the number after n hours have passed and N(o) is the original number which is 15.
The number grown in the 12th hour is the difference in the number after the 11th and the 12th hour. Thus:
15 x 2¹² - 15 x 2¹¹
= 30,720 bacteria
        
             
        
        
        
Answer:
Boiling point of the solution is 100.78°C
Explanation:
This is about colligative properties.
First of all, we need to calculate molality from the freezing point depression.
ΔT = Kf . m . i
As the solute is nonelectrolyte, i = 1
0°C - (-2.79°C) = 1.86 °C/m . m . 1
2.79°C / 1.86 m/°C = 1.5 m
Now, we go to the boiling point elevation
ΔT = Kb . m . i
Final T° - 100°C  =  0.52 °C/m . 1.5m . 1 
Final T° =  0.52 °C/m . 1.5m . 1  + 100°C → 100.78°C
 
        
             
        
        
        
Electrolysis can be used to separate a substance into its original components/elements and it was through this process that a number of elements have been discovered and are still produced in today's industry.