How many {oxidation state} are for {nickel} ?
When does nickel enter an oxidation state?
What is the oxidation state for nickel?
SELECT ( COUNT ( ?o ) AS ?w ) { resource:nickel property:oxidation_state ?o }
SELECT (COUNT(?obj) AS ?objs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q744> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P1121> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
} 

SELECT (COUNT(?obj) AS ?value ) { wd:Q744 wdt:P1121 ?obj }
5