Question: what is the formula of the hydride formed by rubidium
[{'answer': 'RbH', 'provenance': [{'wikipedia_id': '3001409', 'title': 'Rubidium hydride', 'start_paragraph_id': 1, 'start_character': 64, 'end_paragraph_id': 1, 'end_character': 67, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '3001409', 'title': 'Rubidium hydride', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 424, 'bleu_score': 0.9731482306711111, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 6862070921951430386}, 'section': 'Section::::Abstract.'}]}]