Hello, I hope everyone is in good health😊

I often get bewildered regarding “which” and “that” I don't know what to put here.

1- I have found the pen “which/that” I lost.
2- Here is the book “that/which” you lent me.
3- please suggest dictionary “which/that” includes phrasal verbs and idioms.
4- This is the house “which/that” belongs to my uncle.

Question

Hello, I hope everyone is in good health😊

I often get bewildered regarding “which” and “that” I don't know what to put here.

1- I have found the pen “which/that” I lost. 
2- Here is the book “that/which” you lent me.
3- please suggest dictionary “which/that” includes phrasal verbs and idioms.
4- This is the house “which/that” belongs to my uncle.

Answer

In all of these sentences you can use either "which" or "that". I mean you can use "that" or "which" and both the sentences would be correct.