Answer
$90^{\circ}$
Work Step by Step
We know that the angle between two vectors is:
$\theta =\cos^{-1} [ \dfrac{u \cdot v}{||u|| \space ||v|| }]$
Therefore,
$\theta =\cos^{-1} [ \dfrac{(1)(0)+(0)(-2)}{0}]=\cos^{-1} (0)$
So, $\theta =90^{\circ}$
