Give concise explanations in answer

[xD_aQt]

What is the best approach to questions like those?

[Studyinghard]

a) Start off by mentioning the elements present. Then refer to the electrochemical series. As you can see the Calcium ions are below the Sodium. Mention the increasing oxidation strength and how sodium is a stronger oxidant and therefore gets reduced.

b) Mention first that the plastic membrane was porous (is that the word) basically it let some ions to go through. in this case it as the sodium ions which reacted with OH- ions to make sodium hydroxide which is a base and can be used to make something, forget.
 

[toshibaj]

c) when combusting, energy will be provided by all plant matter. However some of this plant matter, such as cellulose, is indigestible by humans and thus does not contribute to energy provided when humans eat the food.