Which of the following situations involves Priority being passed from the player performing the action to another player, I.E. will result in an opportunity for Reactions to be played?

To determine if a situation involves passing priority and creating an opportunity for reactions, you must look for moments where a player has added an item to the chain and then explicitly passes, or where a player is finished performing their discretionary actions and passes priority to the next player.

Per the Core Rules and FAQs, priority is the exclusive right to take discretionary actions (like playing a card or activating an ability). Passing priority is the mechanism by which you invite your opponent to respond to your play or allow the chain to proceed toward resolution.

Situations where Priority is passed:

1. After playing a card or activated ability: When you play a card or activate an ability, you add it to the chain and initially hold priority. You may choose to "hold priority" to play multiple items in a row, or you may choose to pass priority to your opponent. Passing priority creates the immediate opportunity for your opponent to play a [Reaction] to your card.
2. During a Showdown (after playing an action): When a player with "Focus" starts a chain by playing an [Action] or [Reaction] during a showdown, they have technically added the first item to the chain. Even though they have Focus, they still use the same Priority rules as in the Main Phase. Once they pass their priority, the opponent gains the opportunity to add [Reaction] cards to the chain.
3. After an item on the chain resolves: When the chain is not yet empty (because multiple items were added), after the topmost item resolves, priority is granted to a player to add more reactions before the next item resolves. The player who added the item now resolving, or the next player in turn order, will eventually have to pass priority if they wish for the chain to continue resolving.

Key Rules to Remember:

• Holding vs. Passing: You are never forced to pass priority immediately after playing a single card. You can play multiple [Reaction] cards in a row while holding priority. Priority only passes to the opponent when you explicitly choose to pass it (Core Rules 338.1.b, FAQ #8207).
• The "Pass-Pass" Sequence: If you pass priority and your opponent also passes, the top item on the chain resolves immediately. You do not get another opportunity to play a [Reaction] to that specific item once the pass-pass sequence occurs (FAQ #4115, FAQ #7752).
• Priority vs. Focus: Focus is permission to start a chain during a showdown. Priority is the actual right to play the card. A player with Focus cannot play a card unless they also possess Priority (Rule 313.4, FAQ #5481).

If you have specific situations in mind, please describe them! I can clarify whether those specific events trigger a priority window for reactions.