Four test tubes were marked as A,B,C and D . Test tube A had salt, B had sugar ,C had chalk powder and D had sago powder . On adding two drops of iodine solution to the content of each test tube , the one that will turn blue-black will be (a) A , (b) B , (c) C , (d) D
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Iodine turns blue-black in the presence of starch. Therefore the testubes that contain starch are the ones that will turn the iodine into blue-black.
Test tube A is salt- has no starch will not turn blue black
Test tube B is sugar- starch in the form of amylopectin, dissacharides and sucrose do not turn iodine to blue black.
Test tube C is chalk powder- has no starch, iodine will not turn blue-black.
Test tube D has Sago powder- has starch, iodine will turn blue-black.
...therefore the only test tube that will change color is test tube D.
Test tube A is salt- has no starch will not turn blue black
Test tube B is sugar- starch in the form of amylopectin, dissacharides and sucrose do not turn iodine to blue black.
Test tube C is chalk powder- has no starch, iodine will not turn blue-black.
Test tube D has Sago powder- has starch, iodine will turn blue-black.
...therefore the only test tube that will change color is test tube D.
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Iodine turns blue-black in the presence of starch. Among the given options, the test tube containing starch is only Test tube D. Even sugar will not change colour because it contains sucrose and it is a non-reducable sugar. Thus, test tube B will remain the same. Similarly, test tube A and C will also show no changes.
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