Answer
Neither,
$cos^{-1}|\dfrac{-1}{\sqrt {6}}| \approx 114.1 ^{\circ}$
Work Step by Step
$n_1=\lt1,2,-1\gt$ and $n_2=\lt 2,-2,1\gt$
Angle between two vectors: $\theta= cos^{-1}|\dfrac{a.b}{|a||b|}|$
$\theta= cos^{-1}|\dfrac{-3}{\sqrt {6} \sqrt {9}}|$
$\theta= cos^{-1}|\dfrac{-1}{\sqrt {6}}|$
$\theta \approx 114.1 ^{\circ}$
Hence, the two planes are neither parallel nor perpendicular.