I think it should be none of those
higher Ka value= stronger acid
stronger acids have weaker conjugate bases, so the acid with the strongest conjugate base would be acetic acid
The reason being is because it help you better understand what is going on on the graph and help you answer the questions on the graph. hope this helps:)
Answer: Sulphur and Oxygen
Explanation: Sulphate ion is 
. It is polyatomic ion which is formed by the combination of sulphur and oxygen elements in the ratio of 1:4.
It is negatively charged species and thus is named by the name _ate at the end.
It usually exists with positively charged species to get stable. eg: ferrous sulphate (
)
