Final answer:
Email is the leanest communication channel in the hierarchy of media richness as it primarily relies on written text and lacks visual and auditory cues.
Step-by-step explanation:
In the hierarchy of media richness, communication channels can be classified based on their ability to convey information effectively. Media richness refers to the capacity of a communication channel to carry multiple cues, provide immediate feedback, and convey rich information.
Among the given options, email is the leanest communication channel. It primarily relies on written text and lacks visual and auditory cues. Unlike video conference or face-to-face communication, email does not provide immediate feedback and can be asynchronous.