Question

Why does the reactivity of a piece of aluminium metal decrease if it is dipped in $HN{{O}_ {3}}$?

Answer 1

reactivity is a measure of how readily a substance undergoes a chemical reaction. The reaction can involve the substance on its own or with other atoms or compounds, generally accompanied by a release of energy. The most reactive elements and compounds may ignite spontaneously or explosively.

Complete step by step solution:
We have been given aluminium metal,
When aluminium metal is dipped in $HN{{O}_ {3}}$,
The increased number of electron shells results in more shielding and a greater distance between the outer electrons and the nucleus, which reduces the attraction of the electrons to the nucleus. These react by gaining electrons and reactivity decreases as you go down the group.
We need to tell about the change in the reactivity,
Reactivity is the tendency of a substance to undergo chemical reaction, either by itself or with other materials, and to release energy.
When aluminium is dipped in nitric acid a layer of aluminium oxide is formed on the metal. This happens because nitric acid is a strong oxidizing agent. The layer of aluminium oxide prevents further reaction of aluminium.
That’s why the reactivity of aluminium decreases.

Therefore, we can conclude that the reactivity of a piece of aluminium metal decreases if it is dipped in $HN{{O}_ {3}}$.

Note: Nitric acid, also known as aqua fortis, is a highly corrosive mineral acid. The pure compound is colourless, but older samples tend to acquire a yellow cast due to decomposition into oxides of nitrogen and water.