Write equations to represent the following observations: When `NaOH` is added to aqueous `CuSO_(4)` solution, a pale blue precipitate is formed. On adding aqueous `NH_(3)` solution, When `NaOH` is added to give a deep blue solution. If the solution is made acidic with dilute `HNO_(3)`, the colour is converted back to pale blue solution.

Explanation

`Cu^(2+)(aq)+2OH^(-)(aq)rarrunderset("Pale blue ppt.")(Cu(OH)_(2)(s))`
`Cu(OH)_(2)+4 NH_(3)rarr[Cu(NH_(3))_(4)]^(2+)(aq)+2OH^(-)(aq)`
`[Cu(NH_(3))_(4)]^(2+)(aq)+underset(("from " HNO_(3)))(4H_(3)O^(+))rarrunderset("Pale blue solution")([Cu(OH)_(4)]^(2-))+4NH_(4)^(+)(aq)`