In Europe and America, onions are known as "the queen of vegetables". For westerners, "if you don't see onions for a day, you will be in a bad mood for a day." Medical research shows that onion camp

(2) Identification of sugar: starch was identified by iodine solution, and soluble reducing sugar was identified by Fehling reagent.

(4) Experimental steps: ① When identifying soluble reducing sugar, firstly prepare onion tissue sample solution, inject 2ml sample solution into test tube, add 2ml newly prepared Fehling reagent, mix well, heat the test tube in water bath, and observe the color change.

② When identifying starch, prepare onion tissue sample solution, inject 2ml sample solution into the test tube, add 2 drops of iodine solution and observe the color change.

(5) Expected experimental results and conclusions: a. If brick red precipitate is observed in step 1, but blue color does not appear in step 2, it means that the sugar contained in the plump scales of onion is only soluble reducing sugar and contains no starch;

B) If no brick red precipitate is observed in step 1, blue appears in step 2, indicating that the sugar contained in onion scale leaves has no soluble reducing sugar, but only starch;

C. If brick red precipitate is observed in step 1 and blue precipitate is observed in step 2, it means that the sugar contained in the plump scaly leaves of onion contains both soluble reducing sugar and starch.

So the answer is:

(2) iodophor reagent

(4) (1) Prepare onion tissue sample solution, inject 2ml sample solution into the test tube, add 2ml newly prepared Fehling reagent, mix well, heat the test tube in a water bath and observe the color change.

② Prepare onion tissue sample solution, inject 2ml sample solution into the test tube, add 2 drops of iodine solution and observe the color change.

(5) A. If brick red precipitate is observed in step 1, but there is no blue color in step 2, it means that the sugar contained in the plump scaly leaves of onion is only soluble reducing sugar and contains no starch.

B. If no brick red precipitate is observed in step 1, and blue appears in step 2, it means that the sugar contained in onion scale leaves has no soluble reducing sugar, only starch.

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