When a copper wire is left in silver nitrate solution,it is observed that the solution turns bluish green.
$(a)$ Explain the observation.
$(b)$ Write the balanced chemical equation to represent the change taking place.

(N/A) Copper is more reactive than silver. In the reactivity series,it is placed above silver. So,copper displaces silver from its salt.
Observation:
$(i)$ The colour of the solution turns bluish green due to the formation of copper nitrate.
$(ii)$ $A$ greyish-white deposit of silver is observed on the surface of the copper wire.
$(b)$ The balanced chemical equation is:
$Cu(s) + 2AgNO_3(aq) \to Cu(NO_3)_2(aq) + 2Ag(s)$