Concentrated `H_(2)SO_(4)` is added to each of the five test tubes containing (i) NaBr, (ii) sugar, (iii) sulphur powder, (iv) KCl and (v) copper turnings. The test tubes are then heated. Identify in which of the test tubes the following changes will be observed. The observations are: formation of a brown substance which on dilution becomes blue.
Support your answer with the help of a chemical equation in this case.

Explanation

When conc. `H_(2)SO_(4)` is heated with copper turnings placed in the test tube (v), a brown mixture of unreacted copper turnings and white anhydrous copper sulphate is formed. When water is added to the mixture, the solution turns blue due to the formation of hydrated `CuSO_(4)`
`Cu+2H_(2)SO_(4)overset(Delta)toCuSO_(4)+SO_(2)+2H_(2)O`
`CuSO_(4)+5H_(2)Otounderset("(blue)")(CuSO_(4)cdot5H_(2)O` (hydrated copper sulphate)