user: ### NOW ANSWER:
Question: what is the properties of sodium when rubidium is NaCl (2.1)?
Columns: ['Lithium', 'Sodium', 'Potassium', 'Rubidium', 'Caesium']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Lithium', 'Sodium', 'Potassium', 'Rubidium', 'Caesium']
SQL:

assistant: SELECT "Sodium" FROM "Table" WHERE "Rubidium" = 'NaCl (2.1)';