Related To: Property

@kuruva Ravi kishore If Property is missing in the Related To dropdown, this is usually because the DreamHouse Property object is not available in the org where you are doing the challenge.

First confirm you are in the same hands-on org that Trailhead is checking. Then go to Setup -> Object Manager and search for Property.

If you do not see Property, install or re-install the DreamHouse package/app required for the Data Modeling module, then refresh Setup and try again.

If you do see Property, make sure you are creating the field from the Favorite object:

Setup -> Object Manager -> Favorite -> Fields & Relationships -> New -> Master-Detail Relationship -> Related To = Property

Trailhead’s step for this unit specifically says the master-detail relationship should be created on Favorite, with Property selected as the related/master object: 

There is also a similar community post for this exact issue: