Question

In which reaction is nitric acid acting as an oxidizing agent?

Answer 1

Hint: Acids are generally those substances which have pH value less than 7, turn blue litmus paper into red and have sour taste rather than these the main property of an acid it is capable of donating a proton and also we can say that it is capable of forming a covalent bond.

Complete answer:
Nitric acid is a highly corrosive mineral acid represented by the chemical formula $HN{{O}_{3}}$ and the pure compound is generally colorless in nature but the older sample gets turns into yellow colour due to decomposition into oxides of nitrogen and water.
Oxidation is defined as the loss of electrons or we can say that increase in the oxidation state of an atom, ion or molecule while reduction can be defined as the gain of electrons or decreases in the oxidation state of any given atom, ion or molecule. Oxidizing power is the tendency of an element to accept electrons. The greater its ability, the greater will be its oxidizing power. Oxidizing power depends upon the effective nuclear charge it gets decreases down the group and increases across the period.
The main reactions in which nitric acid acts as an oxidizing agent can be shown as follows:
1.${{P}_{4}}+20HN{{O}_{3}}\to 4{{H}_{3}}P{{O}_{4}}+4{{H}_{2}}O+20N{{O}_{2}}$
2. $3Zn+8HN{{O}_{3}}\to 3Zn{{(N{{O}_{3}})}_{2}}+4{{H}_{2}}O+2NO$
Hence these are two reactions in which nitric acid acts as an oxidizing agent.

Note:
The atoms which have greater tendency to accept electrons have greater stability. Oxidizing power is based on the effective nuclear charge which can be defined as the charge felt by the outermost (valence) electrons of an atom after taking into account the number of shielding electrons that surround the nucleus.