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Metals and Non-Metals — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceMetals and Non-Metals3 Marks
Question
When a metal X is treated with cold water, it gives a basic salt Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved.
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Answer

solution The atomic mass of metal $X=56$ - Mass of OH group $=56-17=39 u$. This shows that the metal ' $X$ ' is potassium $( K )$ and the basic salt ' $Y^{\prime}$ ' is potassium hydroxide $( KOH )$. It is formed by reacting potassium with cold water. Hydrogen gas 'Z' evolved in the reaction catches fire.
$2 K(s)+2 H_2 O(aq) \rightarrow 2 KOH(aq)+H_2(g)$

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