Acid Base Concepts And Principles

Step 1: Definition
A Lewis acid is an electron-pair acceptor (electron deficient species).
Step 2: Analysis of }}
In , Boron has only 6 electrons in its valence shell. It is an electron-deficient molecule and can accept an electron pair.
Step 3: Analysis of others
, , and all have lone pairs of electrons that they can donate, making them Lewis bases.
Final Answer: (A)