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MODEL PAPER - 3 [2026] — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceMODEL PAPER - 3 [2026]3 Marks
Question
The atomic number of an element is 20 . Write its electronic configuration. State whether this element is a metal or a non-metal. What is its valency? Write the name and formula of the compound which this element forms with chlorine.
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Answer

The element with an atomic number of 20 is calcium (Ca).
The electronic configuration of calcium is: $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 4 s^{2}$.
Calcium is a metal because it is located in Group 2 (or Group IIA) of the periodic table, which consists of metals known as alkaline earth metals.
The valency of calcium is +2 .
The compound that calcium forms with chlorine is calcium chloride. The chemical formula for calcium chloride is $\mathrm{CaCl}_{2}$.

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