Magnetic flux will be maximum when:A. Magnetic field is perpendicular to the plane area ⃝B. Magnetic field lies parallel to the plane area ⃝C. Area is held at an angle of 45o ⃝D. Magnetic flux density is perpendicular to area vector of the surface ⃝

The magnetic flux (Φ) through a surface is given by the relationship Φ = B⋅A⋅cos(θ), where B is the magnetic field, A is the area, and θ is the angle between the magnetic field direction and the normal (perpendicular) to the surface.

A. Magnetic field is perpendicular to the plane area: In this case, θ = 0 degrees, and cos(0) = 1. So, the magnetic flux is Φ = B⋅A, which is the maximum possible flux for a given magnetic field and area.

B. Magnetic field lies parallel to the plane area: In this case, θ = 90 degrees, and cos(90) = 0. So, the magnetic flux is Φ = 0, which is the minimum possible flux.

C. Area is held at an angle of 45o: In this case, θ = 45 degrees, and cos(45) < 1. So, the magnetic flux is less than the maximum possible flux.

D. Magnetic flux density is perpendicular to area vector of the surface: This is essentially the same situation as option A, just described in different terms. The magnetic flux density is another term for the magnetic field, and if it is perpendicular to the area vector (which is a vector normal to the surface), then θ = 0 degrees and the flux is maximized.

So, the magnetic flux will be maximum when the magnetic field is perpendicular to the plane area, or equivalently, when the magnetic flux density is perpendicular to the area vector of the surface. Therefore, both options A and D are correct.