homework and exercises - Ball Bounce Acceleration at the Point of Bounce

simple question but I wanted to confirm my approach of thinking about the problem.

Question: A rubber ball is dropped from the fifth story of a building and free falls to the ground, after which it bounces and rises back up to the fifth story (for the sake of argument). What is the acceleration of the ball at the point of the bounce?

My Assumptions:
-The ball is in free fall -There is no air resistance -The collision is perfectly elastic

Initial Attempted Answer and Rationale: -I think it should still be g, i.e. ~ 10 m/s^2 [down] as only gravity is at work.

Conceptual Difficulty: -The ball switches direction of velocity. Let's say the velocity vector of the ball immediately after impact is 5m/s [up], and the velocity vector of the ball immediately before impact is 5m/s [down]. If the velocity vector before impact is subtracted from the vector after impact, the resultant vector points upwards and is twice as long.

Second Attempted Answer and Rationale: -The acceleration of the ball on the ground must be ~20 m/s^2 upwards?

Any clarification on whether the first or second attempted answer is correct would be much appreciated.