Study the reaction scheme showing reactions of different substances: starch is hydrolysed by dilute hydrochloric acid to glucose solution; yeast converts glucose to substance A and carbon dioxide; acidified potassium dichromate(VI) converts A to acid B; A and B react to give ester C.

1. aIdentify substance A. [1]
2. bIdentify acid B. [1]
3. cIdentify ester C. [1]
4. dSubstance A is converted to acid B using acidified potassium manganate(VII). What is the role of potassium manganate(VII) in the reaction? [1]
5. eDescribe the colour change observed during this reaction. [2]

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