Question

How many sigma and pi bonds are in `C_4H_6`?

Answer 1

`9sigma + 2pi`.
Nine sigma and two pi bonds are present.

Explanation:

There are a number of isomers of `C_4H_6`, but I'll assume you're talking about 1,3-butadiene, because it's the one Google chose.

1,3-butadiene has four carbon atoms, joined together with two double bonds and a single bond. A double bond is a `pi` and a `sigma`, and a single bond is just a `sigma`. This renders

`2(sigma + pi) + sigma = 3sigma + 2pi`.

There are six hydrogen, each with only a single bond joining them to the carbons, and so this means another `6sigma` bonds are present.

Putting all of this together,

`(3sigma + 2pi) + 6sigma = 9sigma + 2pi`