Question: What flammable gas with a safety classification and labelling of NFPA 704: Standard System for the Identification of the Hazards of Materials for Emergency Response has the highest pKa?
SPARQL (Wikidata): select ?ent where { ?ent wdt:P31 wd:Q21073026 . ?ent wdt:P1117 ?obj . ?ent wdt:P4952 wd:Q51139288 } ORDER BY DESC(?obj)LIMIT 5