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# When a substance 'A' reacts with water, it produces a combustible gas 'B' and a solution of substance 'C' in water. When another substance 'D' reacts with this solution of 'C', it also produces the same gas 'B' on warming but 'D' can produce gas 'B' on reaction with dilute sulphuric acid at room temperature. 'A' imparts a deep golden yelow colour to the smokeless flame of bunsen flame. 'A', 'B' , 'C' & 'D' are respectively

(a) $Na, H_2, NaOH, Zn$
(b) $K, H_2, KOH, Al$
(c) $Ca, H_2, Ca(OH)_2, Sn$
(d) $CaC_2, C_2H_2, Ca(OH)_2, Fe$

Answer: $Na, H_2, NaOH, Zn$
When Na reacts with water, it produces a combustible gas $H_2$ and a solution of $NaOH$ in water.
$Na + 2H_2O \longrightarrow 2NaOH \downarrow + H_2 \uparrow$
When Zn reacts with this solution of NaOH, it also produces the same gas $H_2$ on warming but $Zn$ can produce gas $H_2$ on reaction with dilute sulphuric acid at room temperature.
$Zn + 2NaOH \xrightarrow{\Delta} Na_2ZnO_2 \downarrow + H_2 \uparrow$
$Zn + dil. H_2SO_4 \longrightarrow ZnSO_4 \downarrow + H_2 \uparrow$