Final answer:
In HCN, there is one C-H sigma bond and one C-N sigma bond, as well as two C-N pi bonds, making the total 2 σ bonds and 2 π bonds. The correct option is b).
Step-by-step explanation:
The molecule HCN (hydrogen cyanide) consists of hydrogen (H), carbon (C), and nitrogen (N) atoms. When determining the number of sigma (σ) and pi (π) bonds in HCN it's essential to consider the types of bonds that exist within the molecule.
A single bond is a sigma bond, a double bond consists of one sigma and one pi bond, and a triple bond consists of one sigma and two pi bonds.
In HCN, the bond between hydrogen and carbon is a single bond, which means it's a sigma bond. The bond between carbon and nitrogen is a triple bond, which means it contains one sigma bond and two pi bonds.
Therefore, there are two σ bonds (one C-H bond and one C-N bond) and two π bonds (found within the triple C-N bond). The correct answer to the question of how many σ and π bonds are present in the molecule HCN is: b) 2 σ bonds, 2 π bonds.