Challenge 2: An @Mentioned Comment — Solution Walkthrough

Steps:
  1. Select the relevant paragraph, click the comment icon (or
     Insert > Comment).
  2. Type the open question, then type @ followed by the colleague's
     email address, selecting them from the suggested list that
     appears.
  3. Post the comment.

What happens as a result of the @mention:

The mentioned colleague receives a direct notification (typically by
email) alerting them specifically that they were mentioned in a
comment on this document, with a link straight to that comment's
location — distinct from simply leaving a comment that anyone
viewing the document might eventually happen to notice on their own.

Why a Comment was the correct tool, not a Suggestion:

The situation is a genuine open QUESTION about the paragraph's
content — nothing about the actual text is being proposed as a
change yet, since the answer to the question isn't known. A Comment
is specifically for exactly this: raising something for discussion
without touching the text at all, per this chapter's own Comments-
vs-Suggestions distinction. Using a Suggestion here would require
proposing some SPECIFIC replacement text, which doesn't make sense
when the actual issue is still an open question rather than a
decided edit.

WHY THIS WORKS AS AN ANSWER
------------------------------
This is a direct, concrete instance of this chapter's own core
distinction, combined with the @mention feature specifically
highlighted as a genuine Google-specific addition beyond what Word's
own Comments offer — turning a general discussion note into a
directed, notified request for a specific person's input.