Question

Which of the following acids will not evolve ${H_2}$ gas on reaction with alkali metals?
(A) Hydrazoic acid
(B) Perxenic acid
(C) Boric Acid
(D) None of these

Answer 1

Hint : Alkali metals are very reactive due to the existence of only one electron in their last shell. A lot of compounds of these alkali metals are soluble in water. Usually, alkali metals react with strong acids like hydrochloric acid, nitric acid and sulfuric acid to produce relevant alkali metal salt and to emit hydrogen gas.

Complete Step By Step Answer:
As we know alkali metals are the chemical elements which lie in the s-block of the periodic table which include lithium ( $Li$ ), sodium ( $Na$ ), potassium ( $K$ ), rubidium ( $Rb$ ), cesium ( $Cs$ ), and francium ( $Fr$ ). Alkali metals readily lose their outermost electron from s shell to form cations with positive charge and readily make them highly reactive elements.
Alkali metals release nitrogen gas on reaction with Hydrazoic acid. When an alkali metal reacts with hydrazoic acid, acidification of an azide salt takes place which releases nitrogen ${N_2}$ gas. For example, potassium carbonate reacts with hydrazoic acid to form potassium azide which decomposes to form potassium metal and releases nitrogen gas.
$\begin{gathered} {K_2}C{O_3} + 2H{N_3} \to 2K{N_3} + {H_2}O + C{O_2} \\\ 2K{N_3} \to 2K + 3{N_2} \\\ \end{gathered}$
Perxenic acid is the unstable conjugate acid of the perxenate anion which is formed by the solution of xenon tetroxide. When alkali metals react with Perxenic acid it releases oxygen gas. For instance, reactions are depicted below:
$\begin{gathered} {H_4}Xe{O_6} + 4KOH \to 4{H_2}O + {K_4}Xe{O_6} \\\ {K_4}Xe{O_6} + 2{H_2}S{O_4} \to Xe{O_4} + 2{K_2}S{O_4} + 2{H_2}O \\\ Xe{O_4} \to Xe + 2{O_2} \\\ \end{gathered}$
Boric acid is a weak, monobasic lewis acid of boron. Boric acid may be prepared by reacting borax which is sodium tetraborate decahydrate with a mineral acid and it does not evolve any gas. For instance, the reaction is depicted below:
$KOH + {H_3}B{O_3} \to KB{O_2} + 2{H_2}O$
The formed metal borate on heating dehydrates leading to the formation of tetraborate which can further give rise to boron trioxide.
As a result, among the given options, there is no acid which evolves ${H_2}$ gas.
Hence, the correct option is option (D).

Note :
Generally dilute acids readily react with comparatively reactive metals like magnesium, zinc, aluminium, and iron. The resultant products of this reaction include evolution of hydrogen gas along with salt. For example: Magnesium metal (Mg) can react with the dilute nitric acid resulting in the formation of magnesium nitrate salt and hydrogen gas. The reaction is depicted below:
$Mg + HN{O_3} \to Mg{(N{O_3})_2} + {H_2}$