Aldehydes, Ketones and Carboxylic Acids

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P and Q are isomers of dicarboxylic acid C‌4H‌4O‌4.Both decolorize Br‌2 / H‌2O. On heating, P forms the cyclic anhydride.
Upon treatment with dilute alkaline KMnO‌4, P as well as Q could produce one or more than one from S,T and U.