Alice and Bob would like to communicate with each other using a session key but they do not already have a shared secret key. Which algorithm can they use to exchange a secret key?

The correct answer to the following question will be "Diffie-Hellman".

Explanation:

The symmetric encryption system of Diffie-Hellman enables two individuals or parties with no previous experience of one another to collectively create a mutual secret key across an unprotected stream or network. The above key could also be used with symmetric key encryption to secure subsequent correspondence or communication.

So Bob and Alice will use this type of technique to share a secret key.