Final answer:
The block that most commonly forms anions is the p block. Elements in the p block, specifically Group 17, have a tendency to gain one electron and become anions with a charge of -1.
Step-by-step explanation:
The block that most commonly forms anions is the p block. Anions are negative ions that are formed when a nonmetal atom gains one or more electrons. Elements in the p block, specifically Group 17 (also known as Group VIIA), have a tendency to gain one electron and become anions with a charge of -1. This is because they have seven valence electrons in their outermost energy level and gaining one electron will complete their outer electron configuration to match that of a noble gas.