Q1. [4] § 3.2 CHEMICAL PROPERTIES OF METALS
The melting points and boiling points of some ionic compounds are given below :
Compound | Melting Point (K) | Boiling Point (K)
NaCl | 1074 | 1686
LiCl | 887 | 1600
CaCl₂ | 1045 | 1900
CaO | 2850 | 3120
MgCl₂ | 981 | 1685
These compounds are termed ionic because they are formed by the transfer of electrons from a metal to a non-metal. The electron transfer in such compounds is controlled by the electronic configuration of the elements involved. Every element tends to attain a completely filled valence shell of its nearest noble gas or a stable octet.
Read the following and answer the questions:
- (i) Show the electron transfer in the formation of magnesium chloride. [1]
- (ii) List two properties of ionic compounds other than their high melting and boiling points. [1]
- (iii) Answer (A) or (B): [2]
Previously asked in CBSE board exam
2023 31/4/1 Q37
Generated by claude-sonnet-4-6 · 2026-06-15 06:48 · grounding stimulus
Model Answer
(i) Electron transfer in formation of MgCl₂:
Mg has 2 valence electrons; each Cl needs 1 electron.
Mg → Mg²⁺ + 2e⁻
Cl + e⁻ → Cl⁻ (×2)
So Mg²⁺ + 2Cl⁻ → MgCl₂
(ii) Two properties of ionic compounds:
- They are soluble in water (polar solvents).
- They conduct electricity in molten state or in aqueous solution (due to free ions).
(iii) (The sub-question (A)/(B) options are not printed in the passage provided. Please provide the actual text of option A or B to receive a complete answer.)
Source: Chapter 3 – Metals and Non-metals, Chemical Bonding / Ionic Compounds section
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Explanation
- (i) Examiners expect you to show the dot-structure or ionic equation clearly indicating Mg loses 2e⁻ and each Cl gains 1e⁻. Even a simple equation with charges is accepted.
- (ii) Do NOT repeat high melting/boiling points — the question says "other than." Conductivity and solubility in water are the two standard NCERT properties to cite.
- (iii) Since the A/B options were not included in the extract given, the answer cannot be written. In your actual exam, you will see both options and must choose one — budget roughly 40–50 words for a 2-mark answer.
If a question refers to an image, map, graph or diagram that is not shown here, find the actual CBSE question paper on the CBSE website:
cbse.gov.in.