What kind of intermolecular forces act between a hydrogen cyanide (HCN) molecule and a carbon monoxide molecule?

Dispersion forces

Dipole-Dipole interaction

Explanation:

The London dispersion force refers to the temporary attractive force that acts between the electrons in two adjacent atoms when the atoms develop temporary dipoles. Dispersion forces act between any two molecules even when other intermolecular forces are in operation as long as the molecules are in close proximity to each other.

Now, CO is polar and the HCN is also polar molecule. Hence, dipole - dipole interaction forces  are also in operation and acts between the two molecules in close proximity to each other.

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