Thanks to everyone for their help. If I may concerning my third question. Supposedly only the colours remain and I scratched on the yellow but in so doing left my opponent snookered on the yellow. I assume then he could either have me shoot again or could he not then nominate or elect a free ball, ie/ anything higher than yellow as the yellow. If he could and sunk that higher ball for 2 points is it then respotted to become its actual numeric number and is the yellow still on or does the yellow get removed ? .Does the free nominated ball stay down? Sorry If I confuse anyone as I really appreciate your help.
You seem to be making this circumstance more complicated than it actually needs to be. I will attempt to respond in general terms so that you may apply the same principles in any similar situation...
When a frame of snooker reaches the point at which all of the reds have been removed from the table, that stage is what I refer to as the "end game". During the end game, whenever the striker steps to the table, the ball on is, by definition, the lowest point value ball currently on the table. IF THE OUTGOING STRIKER HAS COMMITTED ANY FOUL, then the incoming player has, or may have, a number of options. Firstly, the incoming striker ALWAYS has the option of putting the offending player back in to take the stroke at hand requiring him to play at the ball on. (In your hypothetical, that would be YELLOW--the offending player being put back in NEVER has the free ball option, he MUST play for the ball on.) Secondly, IF THE OUTGOING STRIKER HAS COMMITTED ANY FOUL and has left the table in such state that the incoming striker is left SNOOKERED on the ball on, then the incoming striker will also have the option of nominating and playing at a free ball in lieu of the current ball on. The free ball will temporarily take the value of the current ball on (in your case, 2 points). If potted, the free ball is spotted and the striker then MUST play at the ball on. (Presumably, in your hypothetical, the striker can nominate any other color for the free ball, pot it, spot it, then play at yellow.) However, it is possible to nominate a free ball, strike it, and then pot the original ball on in a legal stroke. New paragraph to explain.....
Let's say your opponent pots the last red and scratches, foul stroke, there are no longer any reds on the table. Yellow is the ball on. You have ball in hand in the "D". Let's say the brown/yellow are lined up for a perfect plant into the yellow pocket, with yellow closest to the pocket so that yellow is snookered for the incoming player from anywhere within the "D". The incoming striker can then nominate brown as free ball, strike brown, and pot the yellow with the plant. Legal stroke, 2 points and now the green (lowest value ball) is the ball on. All of that sounds complex, but the principle is always the same and the principle is quite simple....when the striker steps to the table, the lowest value ball on the table is the ball on; if a free ball is played and potted, it is re-spotted, and the next ball on will be...guess what....the lowest value ball on the table.
Now, there is another simple principle to bear in mind. When you reach the end game, every ball on MUST be potted with a LEGAL STROKE, otherwise, it will be returned to the table on its spot. For instance, let's say the ball on is yellow. You strike yellow and pot it, but in the same stroke, the cue ball also strikes and pots blue. Foul stroke. The yellow was potted, but it was not potted on a LEGAL stroke so it must be returned to the table on its spot (as well as the blue, of course). Same principle applies for instance, if a ball jumps off the table during the END GAME--foul stroke and the ball is returned to its spot. (This is not the case when reds are on the table. If a red jumps off the table, it is a foul stroke, but the red remains off the table as there is no defined spot to put it on.) In the brown/yellow plant scenario above, even though brown was nominated as free ball, yellow is STILL considered to be a ball on (it is the lowest value ball on the table at the beginning of the stroke) so that, when potted, yellow was the ball on and it was potted on a legal stroke so that it remains in the pocket. (Interesting but rather tricky side note--in the free ball brown/yellow plant scenario above, if BOTH yellow and brown happen to fall into a pocket, it is a LEGAL STROKE but the striker is ONLY credited the score of the original ball on. The free ball is re-spotted with no additional points added and the striker continues the break.)
... is the yellow still on or does the yellow get removed ? .Does the free nominated ball stay down?...
During the end game, no ball can simply be "removed"; it must be potted on a legal stroke. You should clearly understand now that the potted free ball which temporarily took the value of the ball on will be returned to its spot and will become the ball on when it becomes the lowest value ball remaining on the table.
TO SUMMARIZE: There are really only two simple principles that are detailed above:
1) During the end game, the LOWEST VALUE BALL on the table is always considered to be the BALL ON, whether there is a free ball situation or not.
2) During the end game, the BALL ON MUST ALWAYS BE POTTED ON A LEGAL STROKE. Any ball which is either a potted free ball or which is potted or forced off the table during the course of a foul stroke is returned to its spot.