This question tests the ability to determine the morphological pattern (الوزن الصرفي) of an Arabic word.
The word مستشفى derives from the root ش-ف-ي (relating to healing/cure). It comes from the verb استشفى (to seek a cure), which is Form X (استفعل). When we form the noun of place (اسم المكان) or the passive participle from a Form X verb, the prefix است becomes مست, giving the pattern مُستفعَل.
To verify, map the root letters onto the pattern:
مُ - prefix (not from the root)
ست - augmented letters (not from the root)
ش = ف (first root letter)
ف = ع (second root letter)
ى = ل (third root letter)
This gives مُستفعَل, confirming the pattern.
The pattern مفعل applies to simpler three-letter verbs, مُفتعل applies to Form VIII verbs (افتعل), and مفعول is the passive participle pattern for Form I verbs. None of these match the six-letter augmented structure of مستشفى.
