Question

When a substance ‘A’ reacts with water, it produces a combustible gas ‘B’ and a solution of substance ‘C’ in water. While another substance ‘D’ reacts with solution of ‘C’ to produce the same gas ‘B’ on reaction with dilute ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$ at room temperature. ‘A’ imparts a deep golden yellow colour to a smokeless flame on Bunsen burner. Identify ‘A’, ‘B’, ‘C’ and ‘D’ respectively are:
A. ${\text{K, }}{{\text{H}}_2}{\text{, KOH, Al}}$
B. ${\text{Na, }}{{\text{H}}_2}{\text{, NaOH, Zn}}$
C. ${\text{Ca}}{{\text{C}}_{\text{2}}}{\text{, }}{{\text{C}}_2}{{\text{H}}_2}{\text{, Ca}}{\left( {{\text{OH}}} \right)_2}{\text{, Fe}}$
D. ${\text{Ca, }}{{\text{H}}_2}{\text{, Ca}}{\left( {{\text{OH}}} \right)_2}{\text{, Sn}}$

Answer 1

Hydrogen is combustible gas. We have to identify the metal that gives a deep golden yellow colour to a smokeless flame on Bunsen burner and then identify the various reactions that the element ‘A’ undergoes. This approach will make the identification of the compounds easier.

Complete step by step solution:
‘A’ imparts a deep golden yellow colour to a smokeless flame on Bunsen burner.
Sodium on burning generally gives a deep golden yellow colour to a smokeless flame on Bunsen burner. Thus, ‘A’ is sodium $\left( {{\text{Na}}} \right)$ metal.
When a substance ‘A’ reacts with water, it produces a combustible gas ‘B’ and a solution of substance ‘C’ in water.
The reaction of sodium metal with water is as follows:
${\text{2Na}} + {\text{2}}{{\text{H}}_{\text{2}}}{\text{O}} \to {\text{2NaOH}} + {{\text{H}}_{\text{2}}}$
In the reaction, sodium metal reacts with water and sodium hydroxide $\left( {{\text{NaOH}}} \right)$ solution and hydrogen gas $\left( {{{\text{H}}_{\text{2}}}} \right)$ are produced.
Thus, the combustible gas produced ‘B’ is the hydrogen gas $\left( {{{\text{H}}_{\text{2}}}} \right)$ and ‘C’ is sodium hydroxide $\left( {{\text{NaOH}}} \right)$.
Substance ‘D’ reacts with solution of ‘C’ to produce the same gas ‘B’ on reaction with dilute ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$ at room temperature.
Zinc $\left( {{\text{Zn}}} \right)$ on reaction with sodium hydroxide $\left( {{\text{NaOH}}} \right)$ produces hydrogen gas $\left( {{{\text{H}}_{\text{2}}}} \right)$. The reaction is as follows:
${\text{Zn}} + {\text{2NaOH}} \to {\text{N}}{{\text{a}}_2}{\text{Zn}}{{\text{O}}_2} + {{\text{H}}_2}$
Also, zinc $\left( {{\text{Zn}}} \right)$ on reaction with dilute sulphuric acid $\left( {{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}} \right)$ at room temperature produces hydrogen gas $\left( {{{\text{H}}_{\text{2}}}} \right)$. The reaction is as follows:
${\text{Zn}} + {{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}\xrightarrow{{{\text{Room temperature}}}}{\text{ZnS}}{{\text{O}}_{\text{4}}} + {{\text{H}}_2}$
Thus, ‘D’ is zinc $\left( {{\text{Zn}}} \right)$.
Thus, ‘A’ is ${\text{Na}}$, ‘B’ is ${{\text{H}}_2}$, ‘C’ is ${\text{NaOH}}$ and ‘D’ is ${\text{Zn}}$.

**Thus, the correct option is (B) ${\text{Na, }}{{\text{H}}_2}{\text{, NaOH, Zn}}$.

Note: **
Sodium metal burns with a characteristic deep golden yellow coloured flame. Sodium is highly flammable solid and it reacts very violently with air or moist air or water or steam. Hydrogen gas is released during burning of sodium.