The least-to-most arrangement is often used in
a. narration.
b. descriptions.
c. persuasive writing.

I believe the correct option is c. persuasive writing. The least-to-most arrangement wouldn't be the most effective technique in narration, which has its own inherent rules. A narrator doesn't have to list any facts in any order. They can arrange them as they please. Descriptions also don't rely on any particular order, except one that would suit characterization or another artistic purpose. In persuasive writing, the least-to-most or most-to-least arrangement can be an effective device.