How many pixels are there in a Cathode Ray Tube monitor?

There aren't pixels as such. the face of the CRT is coated with phosphors that light up when electrons strike them. The equivalent pixels would be a function of beam size.

Moving on to later color CRTs, there was a mask overlay to force a pixel effect and isolate the RGB beams to one 'pixel' area.

Pixels don't become real until you have a true digital display when there are in fact individual pixels to light up.