Mercury dissolves in concentrated nitric acid, with the evolution of a reddish-brown gas, just as in the reaction shown in figure 5.4 on page 188 for copper. The oxidation state of the mercury after reaction is +2. Write a balanced net ionic equation for the reaction?

2Hg + 4HNO3 ==> 2Hg(NO3)2 + 2NO2 + 2H2O

To write a balanced net ionic equation for the reaction, we need to first understand the reactants and products involved.

Given information: Mercury dissolves in concentrated nitric acid, with the evolution of a reddish-brown gas. The oxidation state of mercury after the reaction is +2.

Let's break down the reaction into two half-reactions, oxidation and reduction:

Oxidation half-reaction:
Mercury (Hg) starts with an oxidation state of 0 and ends with an oxidation state of +2.

Reduction half-reaction:
Nitric acid (HNO3) starts with nitrogen (N) in an oxidation state of +5 and ends with nitrogen (N) in an oxidation state of +2. Oxygen (O) starts with an oxidation state of -2 and ends with an oxidation state of 0.

Now, let's write the balanced net ionic equation by combining the two half-reactions:

Oxidation half-reaction:
Hg → Hg2+ + 2e-

Reduction half-reaction:
HNO3 + 2H+ + 2e- → NO + H2O

Balanced net ionic equation:
Hg + 2HNO3 + 4H+ → Hg2+ + 2NO + 3H2O

In this equation, the mercury (Hg) is oxidized from 0 to +2, and nitrogen (N) is reduced from +5 to +2. The balanced equation shows the formation of mercury ions (Hg2+), nitrogen monoxide (NO), and water (H2O) as products.

Please note that this equation represents a simplified net ionic equation, which only focuses on the species that are actively involved in the reaction. The complete balanced equation might involve additional spectator ions and other species present in the reaction.