I created a new entry for the chemical substance Adenylthiomethylpentose. I decided to add the melting point.
After I input the number Wikidata offers me a box to optionally add a unit. Adding that unit shouldn't be optional and it shouldn't as numbers without unit don't help in this database.
Wikidata knows from the units used for this property-property of melting point that it can have three possible units: kelvin, degrees Celsius. and degree Fahrenheit. It should offer me a menu to select one of them.