Question

When a metal is added to dilute $HCl$ solution, there is no evolution of gas. The metal is:
A.) $K$
B.) $Na$
C) $Ag$
D.) $Zn$

Answer 1

The reactivity series can be used to find out which metal will react with hydrogen or hydrochloric acid to reduce this hydrogen to hydrogen gas. The metal which is below hydrogen in the reactivity series will not reduce hydrogen to hydrogen gas.

Complete step by step answer:
As we know that we can predict any reaction with the help of reactivity series. The reactivity series helps us to predict how metals will react. The more reactive metal is placed at the top of series and less reactive metals at the bottom of the series. The reactivity of metals decreases as we go from top to down in the reactivity series.
For option A.), As we can see that the potassium ($K$) is above the hydrogen in the reactivity series. Therefore, potassium is more reactive than hydrogen and when potassium reacts with hydrogen chloride then it reduces hydrogen of hydrochloric acid into hydrogen gas. This reaction can be given as:
$2K + 2HCl \to 2KCl + {H_2}(g)$
For option B.), As we can see that the sodium ($Na$) is also above the hydrogen in the reactivity series. Therefore, sodium is more reactive than hydrogen and when sodium reacts with hydrogen chloride then it reduces hydrogen or hydrochloric acid into hydrogen gas. This reaction can be given as:
$2Na + 2HCl \to 2NaCl + {H_2}(g)$
For option C.), As we can see that the silver ($Ag$) is below the hydrogen in the reactivity series. Therefore, silver is less reactive than hydrogen. Hence, silver does not react with hydrogen chloride.
For option D.), As we can see that the zinc ($Zn$) is above the hydrogen in the reactivity series. Therefore, zinc is more reactive than hydrogen and when zinc reacts with hydrogen chloride then it also reduces hydrogen of hydrochloric acid into hydrogen gas. This reaction can be given as:
$Zn + HCl \to ZnC{l_2} + {H_2}(g)$

Hence, option C.) is the correct answer.

Note:
Always remember that when silver metal reacts with hydrochloric acid then no reaction takes place this is because silver is less reactive than hydrogen and it cannot reduce hydrogen chloride into hydrogen.