I agree with what you have said.

I believe that which can also be used since we are using the article before dress.

Mary returned the dress, which was torn at one of the seams, to the store.

In the original sentence WHICH refers to the STORE. WHICH can only modify a noun and not a whole clause. The store was not torn (the dress was torn).

The use of THAT is correct.

saurabh2525_gupta wrote:Mary returned the dress to the store, which was torn at one of the seams.

Here WHICH modifies the dress so it should be places next to it. But instead of which, we should use THAT. This is because we need to identify the dress being returned. It can only be identified by essential modifier.

So corrected sentence should be:-
Mary returned the dress that was torn at one of the seams to the store.

I don't think it's necessary to use an essential modifier here; in standard English, it would depend on the context. For example:

"Mary went through all her dresses during Spring Cleaning. She sorted them into three piles based on whether she wanted to keep them. Afterwards, she returned the dress that was torn to the store."

"Mary washed the dress, ironed it, and hung it up in her closet, but then she noticed something off about it, and she returned the dress, which was torn at the seams, to the store."

Each above is correct, although the GMAT would never give that much context. However, I want to point out that THE GMAT DOES NOT ANY LONGER TEST WHICH VS THAT. They used to, but they now consider the rule "controversial" and have removed all such questions from the OG12 and from the test. If you think you see an error along these lines on test day ... ignore it!

SticklorForDetails wrote:

saurabh2525_gupta wrote:Mary returned the dress to the store, which was torn at one of the seams.

Here WHICH modifies the dress so it should be places next to it. But instead of which, we should use THAT. This is because we need to identify the dress being returned. It can only be identified by essential modifier.

So corrected sentence should be:-
Mary returned the dress that was torn at one of the seams to the store.

I don't think it's necessary to use an essential modifier here; in standard English, it would depend on the context. For example:

"Mary went through all her dresses during Spring Cleaning. She sorted them into three piles based on whether she wanted to keep them. Afterwards, she returned the dress that was torn to the store."

"Mary washed the dress, ironed it, and hung it up in her closet, but then she noticed something off about it, and she returned the dress, which was torn at the seams, to the store."

Each above is correct, although the GMAT would never give that much context. However, I want to point out that THE GMAT DOES NOT ANY LONGER TEST WHICH VS THAT. They used to, but they now consider the rule "controversial" and have removed all such questions from the OG12 and from the test. If you think you see an error along these lines on test day ... ignore it!

Hi SticklorForDetails,

Thank you for the update that GMAT no longer tests which vs that.

But if a question comes(to my luck-good/bad) which test which vs that, then please tell me which one shall I choose in the above context and why.