***** NOT A TEACHER *****
A teacher will answer you shortly (soon).
I ONLY wanted to share some IDEAS with you.
1. Please remember that in English, one ALWAYS capitalizes the person pronoun "I."
2. I believe that your first sentence has three possibilities.
a. The check [cheque] that I deposited on the 10th was for 450 pounds.
b. The check which I deposited on the 10th was for 450 pounds.
c. The check, which I deposited on the 10th, was for 450 pounds.
"a" is a defining clause. American English prefers "that" for defining clauses.
"b" is also a defining clause.
"c" is a non-defining clause. (Notice the commas)
I think that it is accurate to say that the appropriate sentence depends on the context (the whole situation).
"The check that / which I deposited on the 9th was for 100 pounds, but the check that / which I deposited on the 10th was for 450 pounds."
I will leave it to someone else to create a situation in which the non-defining sentence would be appropriate.
Student or Learner