The number of C - C sigma bonds present in 1-Butyne is 

3 C–C sigma bonds.

1-Butyne has the structure HC≡C–CH2–CH3. The triple bond between the first two carbons contains one sigma (σ) bond and two pi (π) bonds. Every single C–C bond contributes one sigma bond. So:

• C1≡C2: 1 σ (plus 2 π, which do not count toward sigma)
• C2–C3: 1 σ
• C3–C4: 1 σ

Total C–C sigma bonds = 1 + 1 + 1 = 3.

Step-by-step method to count sigma bonds

1. Write the carbon skeleton: 4 carbons in a straight chain (but-) with a triple bond at carbon-1 (-yne).
2. Identify each C–C connection: C1–C2, C2–C3, C3–C4.
3. Assign bond types: C1–C2 is a triple bond; the others are single bonds.
4. Count σ bonds only: Any single, double, or triple C–C bond contains exactly one σ bond.