Question: na is the symbol for which of the following chemical elements
[{'answer': 'Sodium', 'provenance': [{'wikipedia_id': '26826', 'title': 'Sodium', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 6, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '26826', 'title': 'Sodium', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 823, 'bleu_score': 0.9236266804180681, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7119577813482137184}, 'section': 'Section::::Abstract.'}]}]