Question

Why are the electron affinities of the group 4a elements more negative than those of the group 5a elements?

Answer 1

The electron subshells in the atoms of group 5a elements discourage electron addition.

This is because the subshells in the group 5a elements are already half-filled, which is a more stable electronic configuration that that which would be achieved if another electron was added.
Meanwhile, group 4a elements' subshell becomes half-filled when an electron is added, making them somewhat stable. This means that they prefer electron addition.