Hi,
That is quite an interesting question. Although i'm no expert in sentences, let me give a take.
"in which"/"to which" is a prepositional phrase.
Till date, i have thought of "in which" as an alternative to "where".
E.g.
This is the place where my father lives.
This is the place in which my father lives.
According to me, "in which" is a more formal usage.
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For "to which", i came across an interesting example in an OG question. I'm sure that most of us must have come across such a sentence.
Although i'm making this sentence up, i saw a similar sentence in OG.
E.g.
This is the virus which many people got exposed to --> This one sounds ugly because of the preposition coming at the end.
This is the virus to which many people got exposed --> Sounds better now
This is one of the usages where "to which" is extremely useful.
I hope that these examples give you some idea.
