Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
what is the properties of sodium when rubidium is nacl (2.1)?

### Inputs:
table_name: table, columns: ['Lithium', 'Sodium', 'Potassium', 'Rubidium', 'Caesium']

### Response:
SELECT Sodium FROM table WHERE Rubidium = nacl (2.1)