Final answer:
The correct chromosome arrangement of sex chromosomes in the adults of this new amphibian would be female AB and male AB, similar to the avian sex determination system.
Step-by-step explanation:
The correct chromosome arrangement of sex chromosomes in the adults of this new amphibian would be:
Female: AB
Male: AB
Based on the given information, when the female is heterogametic (AB) and the male is homogametic (AB), the chromosome arrangement would be female AB and male AB. This is similar to the avian sex determination system where the heterogametic female has different sex chromosomes than the homogametic male.