Alka-seltzer is an effervescent antacid which neutralizes the acid of the stomach by generating CO2. The chemical formula of alka-seltzer is C16H17NaO14. In this case, if we are given the mass of the antacid used, then by stoichiometry, mass alka-seltzer * (1/ molar mass of alk-selz) * (1 mol Co2 / 1 mol alk-seltz) * (44 g/molCo2). That is how you get the mass of Co2 produced.
Answer:
The equivalent circuit for the electrode while the electrolyte gel is fresh
From the uploaded diagram the part A is the electrolyte, the part part B is the electrolyte gel when is fresh and the part C is the surface of the skin
Now as the electrolyte gel start to dry out the resistance 
of the gel begins to increase and this starts to limit the flow of current . Now when the gel is then completely dried out the resistance of the gel then increases to infinity and this in turn cut off flow of current.
The diagram illustrating this is shown on the second uploaded image
Explanation:
