Given that we need to find the eccentricity of the ellipse 25x² + 16y² = 400.

⇒ 25x² + 16y² = 400

⇒

⇒

Comparing with the standard form

Here b²>a²

⇒ eccentricity(e) =

⇒

⇒

⇒

∴ The correct option is A