Your answer stands insufficient. Please expound.

To "expound" on something means to explain it (idea, book, etc.) in detail.

"Expound" is a regular verb; therefore, the simple past and the past participle are both "expounded".

The teacher instructed the girl to expound on her thesis statement.

When I tried to expound on my opinion, I could hear points that confused even me.

Few voters could expound on why they wanted one candidate over the other.

The administrator asked his assistant to expound on her reason for handing in her resignation.