A:
Yes, some can be made without p.n. (e.g., the motion To Limit or Extend the Limits of Debate).
Some motions require a two-thirds vote unless p.n. has been given, in which case a majority is sufficient (e.g., the motion To Rescind a motion previously adopted).
Some motions require a two-thirds vote and p.n. or a majority of the entire membership (e.g., the motion To Amend the Bylaws).
For more information about p.n., see RONR pp. 118-121.