In-text Questions — Bonding in Carbon — Carbon and its Compounds

1. 12 marksNCERT Cl-10 Science, In-text Qs after §4.1, Q1

   What would be the electron dot structure of carbon dioxide which has the formula CO₂?

   Hint. Carbon needs 4 shared pairs to complete its octet, and it has exactly two oxygen atoms to share them with.

   Step 1 — Count valence electrons. Carbon has 4 valence electrons; each oxygen atom has 6 and needs 2 more to complete its octet.

   Step 2 — Work out the bonding needed. If carbon formed only single bonds, it could satisfy just 2 of its 4 bonds with one shared pair each to two oxygens, leaving both incomplete. Instead, carbon forms a double bond with each oxygen — sharing 2 electron pairs per oxygen — which uses all 4 of carbon's valence electrons and gives each oxygen the 2 extra electrons it needs.

   Step 3 — Describe the structure. O=C=O, where each double bond is two shared electron pairs, and each oxygen atom keeps 2 lone pairs of non-bonding electrons.

   ✦ Answer: O=C=O — carbon forms a double bond with each oxygen atom (2 shared electron pairs per bond), giving carbon a complete octet and each oxygen its 2 lone pairs plus a completed octet.

   Where students slip. Drawing single bonds between carbon and each oxygen — that would leave both carbon and oxygen short of a full octet; only double bonds on both sides balance the electron count correctly.

2. 22 marksNCERT Cl-10 Science, In-text Qs after §4.1, Q2

   What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint – The eight atoms of sulphur are joined together in the form of a ring.)

   Hint. Each sulphur atom only needs to bond to its two ring neighbours to complete its octet — no double bonds are needed here.

   Step 1 — Count sulphur's valence electrons. Each sulphur atom has 6 valence electrons and needs 2 more to complete its octet.

   Step 2 — Work out the bonding pattern. In the S₈ ring, each sulphur atom forms a single covalent bond with each of its two neighbouring sulphur atoms, contributing one electron to each shared pair.

   Step 3 — Check the electron count per atom. Each sulphur atom then has 2 bonding pairs (shared with its two neighbours) plus 2 lone pairs of its own remaining electrons, which is why every atom in the ring ends up with a full octet.

   ✦ Answer: A ring of 8 sulphur atoms, each joined to its two neighbours by a single covalent bond, with each sulphur atom also carrying 2 lone pairs — giving every atom in the ring a complete octet.

   Where students slip. Trying to give each sulphur atom only one bond (as if it were forming a simple diatomic molecule like O₂) — in the S₈ ring, every atom needs exactly two single bonds, one to each neighbour, to close the ring and complete its octet.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc104.pdf) — five in-text question sets (13 questions total, not 18 as some older manifests claim) plus one end-of-chapter Exercise (15 questions, not 20). Unchanged by rationalisation.. Questions are referenced from the NCERT textbook for identification.