What percent of stars become planetary nebulas?
Over 95% of all stars will become planetary nebulae.
When a star which is less than about 8 solar masses runs out of Hydrogen in its core, the core collapses and Hydrogen fusion starts in a shell around the core. At this point the star expands into a red giant.
During this red giant stage the outer layers of the star get blown away from the hot core. These produces a cloud of gas around the core which is a planetary nebular. Radiation from the core ionises the gasses making them very colourful.
Over 95% of stars fall into the less than 8 solar mass category and will ultimately form planetary nebulae. Our Sun will do so in about 5 billion years time.
The remaining stars are massive. They have a violent end in the form of a supernova explosion. The outer layers of these stars get blasted into space forming a nebula. These nebulae are usually called supernova remnants.