user: Question: Which lowest period's element is Ruthenium?
Columns: ['element', 'group', 'period', 'reaction', 'potential']
Types: ['text', 'real', 'real', 'text', 'text']
Sample row: ['Gold', 11.0, 6.0, 'Au 3+ + 3e − → Au', '1.56 V']
SQL:

assistant: SELECT "period" FROM "Table" WHERE "element" = 'Ruthenium';