Question: predominant product when rb is allowed to react with o2
[{'answer': 'principally RbO , rubidium superoxide', 'provenance': [{'wikipedia_id': '2633283', 'title': 'Rubidium oxide', 'start_paragraph_id': 12, 'start_character': 42, 'end_paragraph_id': 12, 'end_character': 79, 'bleu_score': 1.0, 'section': 'Section::::Synthesis.\n'}]}, {'provenance': [{'wikipedia_id': '2633283', 'title': 'Rubidium oxide', 'start_paragraph_id': 12, 'start_character': 0, 'end_paragraph_id': 12, 'end_character': 78, 'bleu_score': 0.8385766789076251, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1892498057030810918}, 'section': 'Section::::Synthesis.\n'}]}]