Question

A combustible gas is liberated when caustic soda solution is heated with
A.$\,S\,$
B.$\,N{H_4}Cl\,$
C. $\,{I_2}\,$
D. $\,Zn\,$

Answer 1

Caustic soda is nothing but sodium hydroxide $\,(NaOH)\,$. Sodium Hydroxide belongs to the inorganic compound family and is usually encountered at room temperature in the shape of a white solid. Sodium cations and hydroxide anions are composed in this chemical complex. At high temperatures, sodium hydroxide can react with metals to form metal oxides.

Complete step by step answer:
-We know that when acid is reacted with metal we get $\,{H_2}\,$ gas whereas alkaline reacts with few metal gives $\,{H_2}\,$ gas
-The nature in which a metal gives hydrogen with both acid and base, is known as Amphoteric nature.
Let us now analyze each option one by one;
-Sulfur $\,(S)\,$ reacts with sodium hydroxide in the processing of sodium sulphate, sodium sulphide and water. No combustible gas is produced here. Hence, this is not the correct option.
-When Ammonium chloride ($\,N{H_4}Cl\,$) reacts with Sodium hydroxide ($\,NaOH\,$) forms Ammonia ($N{H_3}\,$), water (${H_2}O\,$) and sodium chloride ($NaCl\,$) . Here also no combustible gas is produced. Hence, this option is also not correct.
-When iodine ($\,{I_2}\,$) reacts with sodium hydroxide ($NaOH$) produce sodium iodate ($NaI{O_3}\,$), sodium iodide ($NaI$),and water (${H_2}O\,$). Here also no combustible gas is produced.
-Zinc $\,(Zn)\,$ reacts with sodium hydroxide to form sodium zincate ($\,N{a_2}Zn{O_2}\,$) and hydrogen gas $\,({H_2})\,$. Hydrogen is a highly combustible gas and hence this is the correct option.
So, by this information we can conclude that the correct option is option B.

Additional Information:
$Zn + NaOH\xrightarrow{\Delta }N{a_2}Zn{O_2} + {H_2}$
$Al + NaOH\xrightarrow{\Delta }N{a_2}Al{O_4} + {H_2}$
-When zinc reacts with sodium hydroxide we get sodium zincate in addition of hydrogen gas
-When $Al$reacts with sodium hydroxide we get sodium aluminate in addition of hydrogen gas
Uses of hydrogen:
-From the beginning of the space industry, hydrogen has played an important role as a rocket fuel
-Hydrogen used in a fuel cell allows us to produce electricity directly onboard a vehicle with an electric engine. These "zero-emission" vehicles release only water

Note: Zinc and Aluminium are the two most important amphoteric substances. Since iron has no amphoteric properties, sodium hydroxide does not attack iron at room temperature. Even though sodium hydroxide reacts with amphoteric substances, it is not an amphoteric substance by itself.