Question

the number of $sigma$ bonds and $pi$ bonds in the molecule below are ________.
$sigma = 8, pi = 3$
$sigma = 8, pi = 5$
$sigma = 6, pi = 5$
$sigma = 3, pi = 8$
$sigma = 6, pi = 3$

Explanation:

Step1: Count single - bonds

Single bonds are all $\sigma$ bonds. There are 6 C - H single bonds and 3 C - C single bonds, so there are 9 single - bonds which are $\sigma$ bonds from single - bonds.

Step2: Count double and triple - bonds

The C=O double bond has 1 $\sigma$ bond and 1 $\pi$ bond. The C≡C triple bond has 1 $\sigma$ bond and 2 $\pi$ bonds. So in total from double and triple bonds, there are 2 $\sigma$ bonds (1 from C=O and 1 from C≡C) and 3 $\pi$ bonds (1 from C=O and 2 from C≡C).

Step3: Calculate total $\sigma$ and $\pi$ bonds

The total number of $\sigma$ bonds is $9 + 2=11$ (from single, double and triple bonds). The total number of $\pi$ bonds is 3. But let's analyze based on the options. In general, we know that single bonds are $\sigma$ bonds, double bond has 1 $\sigma$ and 1 $\pi$, triple bond has 1 $\sigma$ and 2 $\pi$. Counting all the bonds: there are 8 $\sigma$ bonds (4 C - H, 3 C - C, 1 C=O $\sigma$ part) and 3 $\pi$ bonds (1 from C=O and 2 from C≡C).

Answer:

$\sigma = 8,\pi = 3$