How many {mean lifetime} are for {neutron} ?
For a neutron, what is the mean lifetime?
What is the mean lifetime of a neutron?
SELECT ( COUNT ( ?x ) AS ?v ) { resource:neutron property:mean_lifetime ?x }
SELECT (COUNT(?obj) AS ?objs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q2348> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P2645> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
} 

SELECT (COUNT(?obj) AS ?value ) { wd:Q2348 wdt:P2645 ?obj }
1