Question

The magnetic flux is maximum when the angle between magnetic field
lines and the line perpendicular to the plane of the area is:

Answer 1

Magnetic flux Φ = B A cosθ, where θ is the angle between B and the area normal. Φ is maximum when cosθ = 1, i.e. θ = 0°. (If you mean magnitude, θ = 0° or 180°; for maximum positive flux θ = 0°.)