"positive action" It was an advertising slogan, used by Colt, to help the model stand out from all the other guns being sold at the time.
Advertising word.
I think you mean colt 1911A1 which was the US military handgun from 1911 to about 1985.
A .45 caliber Colt revolver- a handgun.
The B prefix is just part of the assigned serial number of Colt police positive special revolvers. It was assigned beginning in 1970 with B01001 and ending in 1972 with B59999.
Royal Hong Kong Police
I think that you mean "pistol" instead of "positive". I have one of these and it is indeed a pistol. Was that the question? "Police Positive" was a Colt trade name. If the revolver has a square grip it is probably the model known as the "new police" and if it has a rounded grip it is probably the model known as the civilian "new pocket". It's hard to believe but the little dinky .32 revolvers were the standard Police issue around the turn of the 20th century.
Made for England
If you mean the serial number, it can be found when you open the cyclinder. It is located on the frame at the swivel when the cylinder is opened.
Either the Beretta M9 or the Desert Eagle. Most likely the M9. It depends on what you mean. If you mean America's military, the primary handgun is the Beretta M9, but if you mean in general, the Glock is the most common. About 65% of police departments in the U.S. use Glock, and probably about that same amount in competitive practical shooting.
A colt is a young horse.
You will have to define what you mean by "popular". Do you mean by price? Do you mean by resale value? Do you mean by actual use? Do you mean with civilians, military or police? In the retail consumer market, the .380 that is currently selling the most often is the Ruger LCP, if that is what you mean.
It depends on the state, and on what you mean. If you mean a license to carry a handgun, most, but not all states require you to be at least 21.