MPSC 2025 Prelims Paper-I · Question 66 of 100

Correct — option (4), Only b (ionic bond). Magnesium is a metal from Group 2 (the alkaline earth metals) with two electrons in its outermost shell and a low electronegativity, while chlorine is a highly electronegative non-metal from Group 17 that needs just one more electron to complete its outer shell. When magnesium reacts with chlorine, each magnesium atom loses its two outer electrons — one to each of two chlorine atoms — to attain the stable noble-gas electron configuration of neon, while each chlorine atom gains one electron to attain the stable configuration of argon. This complete transfer of electrons, rather than any sharing of them, produces a positively charged magnesium ion (Mg2+) and two negatively charged chloride ions (Cl-), and the compound MgCl2 is held together by the strong electrostatic force of attraction between these oppositely charged ions. That electrostatic attraction between ions formed by complete electron transfer is, by definition, an ionic (or electrovalent) bond, which is exactly what statement b describes. The large electronegativity difference between a Group 2 metal and a Group 17 non-metal is the standard textbook condition for ionic bonding, and MgCl2, like most metal-halide salts, is a classic example of it — a white crystalline solid with a high melting point and good electrical conductivity in the molten or dissolved state, all properties consistent with an ionic lattice.

• (1)Only d — A metallic bond is the electrostatic attraction between positive metal ions and a shared 'sea' of delocalised electrons, and it forms only between atoms of metals bonded to each other, as in a block of pure magnesium or an alloy. MgCl2 is a compound between a metal and a non-metal, not metal atoms bonded to other metal atoms, so no metallic bond is involved at all; the bonding here is between Mg2+ and Cl- ions, which is ionic, not metallic.
• (2)Only a — A covalent bond forms when two atoms — typically two non-metals with comparable electronegativities — share a pair of electrons, as in Cl2 or H2O. Magnesium and chlorine do not share electrons; magnesium's low electronegativity and chlorine's high electronegativity favour a complete transfer of electrons rather than sharing, which is precisely the ionic mechanism, not the covalent one. Selecting covalent bonding here mistakes the general idea of 'atoms bonding' for the specific electron-sharing mechanism that covalency requires.
• (3)Only a and c — This combines covalent bonding (already wrong, as explained above) with coordinate covalent bonding, which is also inapplicable here. A coordinate (or dative) covalent bond is a special case of covalent bonding in which both shared electrons come from just one of the two bonding atoms — as seen in the ammonium ion (NH4+) or in ammonia-borane adducts — but it still involves sharing electrons between atoms, not the complete transfer of electrons from a metal to a non-metal. Since MgCl2 forms by electron transfer producing discrete Mg2+ and Cl- ions, neither of the two covalent-type bonds in this pair actually describes it.

Chemical bonding between two elements is largely governed by the electronegativity difference between them and by how many electrons each needs to reach a stable, noble-gas-like outer shell. When a metal with low ionisation energy (like magnesium) meets a non-metal with high electron affinity (like chlorine), the energetically favourable outcome is for the metal to lose its valence electrons entirely rather than share them, forming a cation, while the non-metal gains those electrons to form an anion. The oppositely charged ions then arrange themselves into a rigid, repeating three-dimensional lattice held together by strong electrostatic (Coulombic) forces — this is ionic bonding. Covalent bonding, by contrast, occurs between atoms of similar electronegativity (typically two non-metals) that share electron pairs rather than transferring them outright, and metallic bonding occurs specifically between metal atoms sharing a common pool of delocalised electrons. MgCl2 is formed from one Group 2 metal and two Group 17 non-metal atoms with a large electronegativity gap, placing it squarely in the ionic category.

MPSC's general science section frequently tests the basic classification of chemical bonds — ionic, covalent, coordinate covalent, and metallic — using simple, familiar compounds like MgCl2, NaCl or CaCl2 to see whether a candidate can correctly match a bond type to the elements involved rather than merely recite bond definitions in the abstract. The four bond types offered as statements here are deliberately the standard textbook set, and the question rewards recognising the specific combination (a reactive metal plus a highly electronegative non-metal) that produces ionic bonding, rather than defaulting to 'covalent' simply because two different elements are combining.

• Magnesium (Group 2) has two valence electrons and low electronegativity; chlorine (Group 17) has seven valence electrons and high electronegativity.
• MgCl2 forms by magnesium losing two electrons (one to each chlorine atom), producing Mg2+ and two Cl- ions.
• The resulting compound is held together by electrostatic attraction between oppositely charged ions — an ionic (electrovalent) bond.
• Covalent bonds involve sharing electrons between atoms of similar electronegativity, typically two non-metals, unlike MgCl2's electron transfer.
• Metallic bonds occur only between metal atoms sharing delocalised electrons, and do not apply to a metal-nonmetal compound like MgCl2.

• Assuming any bond between two different elements must be covalent simply because two different atoms are joining
• Confusing coordinate covalent bonding (electron sharing where both electrons come from one atom) with ionic bonding (electron transfer)
• Applying metallic-bond reasoning to a metal-nonmetal compound, when metallic bonding requires metal atoms bonded to other metal atoms
• Overlooking the large electronegativity gap between Group 2 metals and Group 17 non-metals as the deciding factor for ionic character

MPSC chemistry questions on bonding typically present a familiar compound and a list of the standard bond types, testing whether a candidate can correctly apply the electronegativity-difference rule to pick ionic bonding for metal-nonmetal compounds rather than defaulting to covalent or overcomplicating with coordinate/metallic options.

No directly related past PYQ was found.

• practice — not a real PYQ

  Which of the following pairs of elements is most likely to form an ionic bond ?

  • (a)Chlorine and Chlorine
  • (b)Carbon and Hydrogen
  • (c)Sodium and Chlorine
  • (d)Oxygen and Hydrogen

  Answer(c) Sodium and Chlorine — a reactive Group 1 metal with low electronegativity and a highly electronegative Group 17 non-metal favour complete electron transfer, forming Na+ and Cl- ions held together by an ionic bond, as in common salt (NaCl).

• practice — not a real PYQ

  In the formation of MgCl2, what is the charge on the magnesium ion after bonding ?

  • (a)Mg+
  • (b)Mg2+
  • (c)Mg2-
  • (d)Mg is neutral, only chlorine ionises

  Answer(b) Mg2+ — magnesium loses both its valence electrons (one to each chlorine atom) to attain a stable noble-gas configuration, forming a doubly positive Mg2+ ion.