That tv's used 3 light guns for picture, one green, red, and blue? Instead according to this forum, it's only one gun that shoots the color on the screen...It there a 3 gun variant?

Also, are ALL standard def tv's the same resolution? In other words, does standard def=640x480i? Are there SDtv's that can show in progressive scan for 480p?

Also, are ALL standard def tv's the same resolution? In other words, does standard def=640x480i? Are there SDtv's that can show in progressive scan for 480p?

Each standard def tube will will have its own resolution. 480i X 640 is the format.
If a set can so 480p, then improving it to 540p means it can do the 1080i format. Then this will be marketed as a HDTV.

In a color CRT (tube) 3 electron guns, one for each color, shoot electrons at the screen, and make the appropriate phosphor dot glow. The beams are scanned over the tube by the Yoke coil mounted on the tube.

I think maybe you are getting CRTs mixed up with rear projection. Rear projection uses 3 tubes with 3 guns,CRTs use only 1 gun.

There are 3 individual guns, attached together in one assembly, usually "in line", sometimes in "delta gun" arrangement, inside the CRT neck. 3 Filaments, 3 Cathodes..There is a picture of Sony's in-line gun assembly here, note 3 holes:
https://www.ad.no/pdf/Sony/@%20fdtrin.pdf
If 1 filament fails you lose one color. (A projector has 3 individual tubes with a single gun in each, because they have only one color per tube.)

You are correct, except that the delta arrangement is common on "regular" aka shadow mask CRTs which also have the phosphors laid out in triads, while Sony Trinitron (or aperture grille) tubes use the "in line" arrangement for both electron guns and screen phosphors.

Different manufacturers have used many different gun designs. There's no point in this argument...

But all successful ones have 3 guns inside. :) There were experiments to make a true one-gun color CRT:

http://www.earlytelevision.org/chromatron.html

Looks like the chassis had to pull the beam sideways at the screen..

That was an interesting read, thank you. :)