See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Concept: Secondary (2°) carbon atoms in aromatic/fused ring systems are carbons bonded to exactly two other carbon atoms. A 2° hydrogen is a hydrogen attached to a secondary carbon (a carbon bonded to two other carbons). In the context of aromatic hydrocarbons, this classification applies to ring junction carbons and substituted positions differently from terminal positions. Step 1: Identify the structure. The compound is 2-chloronaphthalene. Naphthalene has 10 carbons in a fused bicyclic system. With Cl at position 2, one hydrogen is replaced by Cl. Step 2: Classify carbons in naphthalene numbering. Naphthalene carbons: positions 1,2,3,4,5,6,7,8 are peripheral (each bonded to 2 ring carbons and 1 H in unsubstituted naphthalene), and positions 4a and 8a are the ring junction carbons (each bonded to 3 ring carbons, no H). Ring junction carbons (4a, 8a) are 3° carbons with no H. Step 3: In 2-chloronaphthalene, C2 bears Cl instead of H. The peripheral carbons bonded to exactly 2 carbon atoms are: C1, C2, C3, C4, C5, C6, C7, C8. These are all 2° carbons. C4a and C8a are 3° (bonded to 3 carbons). Step 4: Count 2° H atoms. Among the 2° carbons (C1–C8), C2 has Cl so contributes 0 H. The remaining seven peripheral carbons (C1, C3, C4, C5, C6, C7, C8) each have one H. That gives 7 hydrogen atoms on 2° carbons. Step 5: Verify other options fail. (a) 2 — too few; (b) 5 — incorrect count; (d) 8 — would require all peripheral carbons including C2 to have H, but C2 has Cl. Therefore, the correct answer is C.