3 marksShort AnswerSection A

An element ‘X’ belong to 3rd period and group 13 of the Modern Periodic Table.

(a) Determine the valence electrons and the valency of ‘X’.

(b) Molecular formula of the compound formed when ‘X’ reacts with an element ‘Y’ (atomic number = 8).

(c) Write the name and formula of the compound formed when ‘X’ combines with chlorine.

Q: An element ‘X’ belong to 3rd period and group 13 of the Modern Periodic Table. (a) Determine the valence electrons and the valency of ‘X’. (b) Molecular formula of the compound formed when ‘X’ reacts with an element ‘Y’ (atomic number = 8). (c) Write the name and formula of the compound formed when ‘X’ combines with chlorine.

(a) **Valence electrons and Valency of 'X':** Element 'X' has $3$ valence electrons and its valency is $3$. (b) **Molecular formula with 'Y' (Oxygen):** The molecular formula of the compound formed is $X_2Y_3$ (which corresponds to Aluminium oxide, $Al_2O_3$). (c) **Name and formula with Chlorine:** The compound formed is **Aluminium chloride** and its formula is $AlCl_3$ (or $XCl_3$).

Metals and Non-metals

Valency and Chemical Formula of Compounds

Official Answer

(a) Valence electrons and Valency of 'X': Element 'X' has $3$ valence electrons and its valency is $3$ .

(b) Molecular formula with 'Y' (Oxygen): The molecular formula of the compound formed is $X_2Y_3$ (which corresponds to Aluminium oxide, $Al_2O_3$ ).

(c) Name and formula with Chlorine: The compound formed is Aluminium chloride and its formula is $AlCl_3$ (or $XCl_3$ ).

valence electrons 3valency 3X2Y3Al2O3Aluminium chlorideAlCl3

Marking Scheme

1State that valence electrons = 3 and valency = 3 for element 'X' (1 mark)
2Derive the molecular formula $X_2Y_3$ (or $Al_2O_3$ ) with explanation (1 mark)
3State the name as Aluminium chloride and formula as $AlCl_3$ (or $XCl_3$ ) (1 mark)

Hint

Identify element 'X' as Aluminium ( $Al$ ) and element 'Y' as Oxygen ( $O$ ). Use the criss-cross method with their respective valencies.

Quick Oral Answer

Element X is Aluminium. It has 3 valence electrons, a valency of 3, and forms an amphoteric oxide with the formula $Al_2O_3$ .

Analysis & Explanation

This question connects the periodic classification of elements with the chemical properties of metals from Chapter 3. Aluminium ( $Al$ ) is a key metal discussed in the text, specifically regarding its amphoteric oxide ( $Al_2O_3$ ) and its reaction with oxygen.

Common Mistakes

1Writing the formula of the oxide as XY3 instead of X2Y3.
2Forgetting to name the compound in part (c) and only writing the formula.

Interesting Facts

Aluminium oxide ( $Al_2O_3$ ) is amphoteric, meaning it can react with both acids (like $HCl$ ) and bases (like $NaOH$ ) to produce salt and water. This is a unique property of certain metal oxides!

Spotted a mistake or something unclear?

Tell us — we fix reported answers fast.

Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2016?

This question carries 3 marks in the CBSE Class 10 Science 2016 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Metals and Non-metals" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Valency and Chemical Formula of Compounds" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2016 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2016 paper.