See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1: Identify the structure of 1-buten-3-yne (but-1-en-3-yne). The IUPAC name '1-butene 3-yne' refers to a 4-carbon chain with a double bond at C1 and a triple bond at C3. The structure is: CH2=CH-C≡CH. Step 2: Count all sigma bonds. - C1-C2 (part of double bond): 1 sigma - C2-C3 (single bond): 1 sigma - C3-C4 (part of triple bond): 1 sigma - C1 has 2 H atoms: 2 sigma (C1-H bonds) - C2 has 1 H atom: 1 sigma (C2-H bond) - C4 has 1 H atom: 1 sigma (C4-H bond) Total sigma bonds = 1 + 1 + 1 + 2 + 1 + 1 = 7 sigma bonds. Step 3: Count all pi bonds. - C1=C2 double bond contributes 1 pi bond - C3≡C4 triple bond contributes 2 pi bonds Total pi bonds = 1 + 2 = 3 pi bonds. Step 4: Verify the answer: 7 sigma and 3 pi bonds, which matches option (b). Step 5: Why other options fail: - (a) 5 sigma and 5 pi: Incorrect count of both. - (c) 8 sigma and 2 pi: Overcounts sigma, undercounts pi. - (d) 6 sigma and 4 pi: Undercounts sigma, overcounts pi. Therefore, the correct answer is B.