In-text Questions — Ionic Compounds — Metals and Non-metals

1. 13 marksNCERT Cl-10 Science, In-text Qs after §3.3, Q1

   (i) Write the electron-dot structures for sodium, oxygen and magnesium. (ii) Show the formation of Na₂O and MgO by the transfer of electrons. (iii) What are the ions present in these compounds?

   Hint. Count valence electrons first — sodium and magnesium are in groups 1 and 2, oxygen is in group 16.

   Step 1 — (i) Electron-dot structures (valence electrons only). Sodium (Na): one dot around the symbol (1 valence electron). Magnesium (Mg): two dots (2 valence electrons). Oxygen (O): six dots (6 valence electrons, needing 2 more for a stable octet).

   Step 2 — (ii) Formation of Na₂O. Each of two sodium atoms loses its one valence electron (Na → Na⁺ + e⁻), and one oxygen atom gains both of those electrons to complete its octet (O + 2e⁻ → O²⁻). The resulting ions combine as 2Na⁺ + O²⁻ → Na₂O.

   Step 3 — Formation of MgO. One magnesium atom loses both its valence electrons (Mg → Mg²⁺ + 2e⁻), and one oxygen atom gains them (O + 2e⁻ → O²⁻), giving Mg²⁺ + O²⁻ → MgO.

   Step 4 — (iii) Ions present. Na₂O contains Na⁺ and O²⁻ ions, since that's what the electron transfer in Step 2 produced. MgO contains Mg²⁺ and O²⁻ ions.

   ✦ Answer: Na has 1 valence electron, Mg has 2, O has 6. Na₂O forms from 2Na⁺ + O²⁻; MgO forms from Mg²⁺ + O²⁻. Ions present: Na⁺ and O²⁻ in Na₂O; Mg²⁺ and O²⁻ in MgO.

   Where students slip. Giving oxygen only one dot pattern that doesn't add up to 6 valence electrons — oxygen is in group 16, so it starts with 6 valence electrons and needs exactly 2 more to reach a stable octet, which is why it always takes 2 electrons per atom in these reactions.

2. 22 marksNCERT Cl-10 Science, In-text Qs after §3.3, Q2

   Why do ionic compounds have high melting points?

   Hint. Melting means overcoming whatever force holds the particles together — think about how strong that force is for oppositely charged ions packed in a lattice.

   Step 1 — Recall the structure of an ionic compound. Ionic compounds are made of positive and negative ions held together by strong electrostatic forces of attraction throughout a rigid lattice.

   Step 2 — Connect this to melting. Melting means overcoming these attractive forces enough to let the ions move freely, and since the inter-ionic attraction is strong, a considerable amount of energy (high temperature) is needed to break it.

   ✦ Answer: Ionic compounds have high melting points because a large amount of energy is needed to overcome the strong electrostatic forces of attraction holding the oppositely charged ions together in the crystal lattice.

   Where students slip. Explaining this in terms of 'strong bonds' without naming the actual force — the specific reason is electrostatic attraction between oppositely charged ions, not a vague notion of bond strength.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc103.pdf) — five in-text question sets (15 questions total, not 18 as some older manifests claim) plus one end-of-chapter Exercise (16 questions, correctly counted). Unchanged by rationalisation.. Questions are referenced from the NCERT textbook for identification.