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A sodium salt of an organic acid, denoted as X, gives brisk effervescence on treatment with concentrated H2SO4. X also forms a white precipitate with acidified aqueous CaCl2, and this precipitate decolourises acidic KMnO4 solution. Identify X.

1. C6H5COONa
2. HCOONa
3. CH3COONa
4. Na2C2O4

Correct answer: Na2C2O4

Solution

X = Na2C2O4 (sodium oxalate). With conc. H2SO4 it gives brisk effervescence (CO + CO2), with acidified CaCl2 it forms insoluble white CaC2O4, and oxalate is a reducing agent that decolourises acidic KMnO4. Sodium formate fails because calcium formate is water-soluble (no white precipitate).

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