I believe the answer is C
The solution is 45.7 % (NH₄)₂CO₃ by mass.
Mass of solution = 0.0332 kg + 0.0395 kg = 0.0727 kg
% (NH₄)₂CO₃ = Mass of (NH₄)₂CO₃/Total mass × 100 % = 0.0332 kg/0.0727 kg × 100 % = 45.7 %
Answer:
6.25 X10^{-9} = Ka

Explanation:
The ionic equation for the hydrolysis of the cation of the given salt will be:

The expression for Ka will be:
Ka = ![\frac{[H^{+}][MOH]}{[M^{+}]}](https://tex.z-dn.net/?f=%5Cfrac%7B%5BH%5E%7B%2B%7D%5D%5BMOH%5D%7D%7B%5BM%5E%7B%2B%7D%5D%7D)
As given that the concentration of the salt is 0.1 M and pH of solution = 4.7, we can determine the concentration of Hydrogen ions from the pH
pH = -log [H⁺]
[H⁺] = antilog(-pH) = antilog (-4.7) = 2 X 10⁻⁵ M = [MOH]
Let us calculate Ka from this,
Ka = 
The relation between Ka an Kb is
KaXKb =10⁻¹⁴

Electrical?
Hope this helps