These Fake Dragon Eggs are given to you by Solaufein if Gorion's Ward spared him in chapter 5 of Baldur's Gate II: Shadows of Amn and Baldur's Gate II: Enhanced Edition. Solaufein gives you these eggs to switch them with the real Dragon Eggs which Phaere plans to sacrifice.
With these, Matron Mother Ardulace and Phaere's attempts to summon the Lesser Demon Lord will backfire if you give them Phaere's fake eggs and these eggs, respectively. These eggs are useful in deceiving Phaere, escaping Ust Natha without combat and returning the real Dragon Eggs to Adalon.
This is an optional plot element available as part of the The Drow Summoning Ritual questline.
Description[]
“ | These are the false dragon eggs given to you by Solaufein. | ” |