Question

whether the resultant of two vectors of unequal magnitude be zero?

Answer 1

two vectors with different magnitude will never add up to zero no matter what their directions are.
but three vectors or more can get you a zero vector.
consider a displacement of 3 m east, 4m north and 5m 225 degree (take the degree anticlockwise). the resultant will be zero.
consider this one too.
displacements are, 5m east, 5m north, 5m west, and 5m south. this will be a square (head to tail method) and give you zero displacement.