Final answer:
In a thymocyte, the β chain can have up to four potential attempts for successful rearrangement, with two attempts per each of the two loci.
Step-by-step explanation:
The β chain of a thymocyte can have multiple attempts at successful rearrangement during T cell development. Each thymocyte initially has two copies of the β chain gene (one from each parent). During the development process in the thymus, these genes undergo rearrangement to generate a functional T-cell receptor (TCR). Each chain can attempt rearrangement a couple of times if the initial rearrangement is unsuccessful. For the β chain, there are two loci, and each can attempt rearrangement. If both attempts fail at one locus, the thymocyte can try the second locus, leading to up to four potential attempts (two attempts per locus).