hello your question is incomplete attached below is missing part
answer : Pauli's exclusion principle
Explanation:
The principle that was disobeyed is <em>Pauli's exclusion principle</em> this is because the Pauli's exclusion principle states that no two electrons can have the same set of quantum number.
In Box A the two electrons , have the same spin which means they have the same quantum number ( disobeys Pauli's exclusion principle )
When a carboxylic acid is treated with an alcohol and an acid catalyst, an ester is formed (along with water). This reaction is called the Fischer esterification.