Please explain this question experts

Dear Student,
At the two magnetic poles, the magnetic needle rests vertically.
Hence, at poles, $\delta = {90}^0$
As, Horizontal component, H = R cos $\delta = 0^0$
And at a place on the magnetic poles, earth's magnetic field is perpendicular to the surface of earth, i.e., vertical.
Therefore, angle of dip ($\delta$) = 90⁰
The angle that a magnetic needle makes with the horizontal plane at any specific location is dip angle.

Hence, a magnetic needle free to rotate in a vertical plane orients itself vertical at the poles of the earth because at poles horizontal component of  earth's field is zero there.

Therefore, both assertion and reason are correct and reason is correct explanation of assertion (option i).

Regards