Question

An example of reversible reaction is :
A.) $Pb(N{O}_3{)}_2+2NaI\to Pb{I}_2+2NaN{O}_3$
B.) $AgN{O}_3+HCl\to AgCl+HN{O}_3$
C.) $2Na+2H_{2}O\to 2NaOH+H_2$
D.) $KN{O}_3+NaCl\to KCl+NaN{O}_3$

Answer 1

Hint:If in the products of a chemical reaction, some of the product is precipitated then the reverse reaction will not be possible. Also, when the product is a gas then also the reversible reaction will not be possible.

Complete step by step answer:
In this question, by reversible reaction we mean a reaction in which the reactants and products can again react to form the reactants. A reversible reaction is the process of making reactants from the products. If in a chemical reaction, any of the product is missed or if any of the product cannot react again then the reaction will be irreversible. There can be some cases when the reaction cannot be reversible. First, if there is any precipitate present in the product then that will not react again with the product to make it reactant and second is when any gas is present in the product then that will evaporate so it will not react again with the product to make it reactant. Hence, these two conditions make the reaction irreversible. Also, ionic exchange reactions are always reversible reactions.
For option A.)
$Pb(N{O}_3{)}_2+2NaI\to Pb{I}_2+2NaN{O}_3$
In this reaction, lead iodide ($Pb{I}_2$) is a precipitate and this precipitate stabilizes the reaction and makes it irreversible.
For option B.)
 $AgN{O}_3+HCl\to AgCl+HN{O}_3$
In this reaction, Silver chloride ($AgCl$) is a precipitate and this precipitate stabilizes the reaction and makes it irreversible.
For option C.)
$2Na+2H_{2}O\to 2NaOH+H_2$
In this reaction, hydrogen($H_2$) gas is produced which will evaporate and no more present in the reacting system and make it irreversible.
For option D.)
$KN{O}_3+NaCl\to KCl+NaN{O}_3$
This given reaction is an ion exchange reaction because here nitrate($N{O}_3^{-}$) and chloride($C{l}^{-}$) ions are exchanged between the sodium and potassium. Hence, it is a reversible reaction.
Hence the correct option is D.

Note:
Always remember that an ion exchange reaction is always a reversible reaction. In ion exchange reaction, two substances (each consisting of positively and negatively charged species called as ions) exchange one or more ionic components between them.