The letter ⟨c⟩ is silent when it follows ⟨s⟩ before ⟨e⟩, ⟨i⟩, or ⟨y⟩. The pair is pronounced just as /s/.
Two ways to see this: You can think of ⟨sc⟩ as a silent ⟨c⟩, or as an unusual spelling of /s/ — see the
S sound page. Both are valid ways to understand it.