How many {refractive index} are for {water} ?
Waters refractive index is?
What is the refractive index for water?
SELECT ( COUNT ( ?r ) AS ?d ) { resource:water property:refractive_index ?r }
SELECT (COUNT(?obj) AS ?objs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q283> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P1109> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
} 

SELECT (COUNT(?obj) AS ?value ) { wd:Q283 wdt:P1109 ?obj }
6