Final answer:
The lowest channel richness among the given options is written memos.
Step-by-step explanation:
The lowest channel richness among the given options is c) Written memos. Channel richness refers to the ability of a communication channel to convey information effectively. Face-to-face communication is the richest channel as it allows for immediate feedback, non-verbal cues, and rich contextual information. Video conferencing is also rich as it allows for visual and verbal communication. Written memos, on the other hand, lack the richness of tone, body language, and immediate feedback. Email communication, although less rich than face-to-face or video conferencing, still allows for real-time messaging, attachments, and some level of interactivity.