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Periodic Classification of Elements — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10SciencePeriodic Classification of Elements3 Marks
Question
An element ‘X’ (Atomic number = 20) burns in the presence of oxygen to form a basic oxide.
  1. Identify the element and write its electronic configuration.
  2. State its group number and period number in the Modern Periodic Table.
  3. Write a balanced chemical equation for the reaction when this oxide is dissolved in water.
✓

Answer

We are given that the element is present in the $2^{\text {nd }}$ group and the $4^{\text {th }}$ period.
i. Therefore this element is Calcium. Its atomic number is 20 and its electronic configuration is 20 .
ii. Its electronic configuration is $2,8,8,2$.
iii. When calcium oxide is dissolved in water, calcium hydroxide is formed. Following is the equation,
$CaO+H_2 O \rightarrow Ca(OH)_2$

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