11973
The monatomic plumbide ion ( Pb ) is unknown , and indeed its formation is predicted to be energetically unfavourable ; alkali metal plumbides have complex Zintl ions , such as .
 Zintl
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Zintl