Identify the kind of the underlined clause in the following sentence:…

The correct answer is Option (3) → Noun clause

The underlined part answers “The warden does not know what?”, so it is the object of “know”, even though it begins with “when”.

Clause	What it does	Example
(1) Adjective clause	describes a noun just before it	Diwali is the day when our whole family meets.
(2) Adverb clause	tells when, where, why or how the action of the main verb happens	Call me when you reach the station.
(3) Noun clause (answer)	does the work of a noun, for example the object of a verb	Nobody knows where Raju hid the keys.
(4) Principal clause	the main clause; it makes sense on its own	The match was stopped because the light was poor.