The coplanar points  $\left(3,2,5\right),\left(2,1,1\right),\left(-1,4,1\right),\left(0,5,5\right)$ form a

Given points are  $A\left(3,2,5\right),B\left(2,1,1\right),C\left(-1,4,1\right),D\left(0,5,5\right)$

The lengths of the sides 

$\begin{array}{c}AB=\sqrt{1+1+16}=\sqrt{18}\\ BC=\sqrt{9+9+0}=\sqrt{18}\\ AC=\sqrt{16+4+16}=\sqrt{36}\\ BD=\sqrt{4+16+16}=\sqrt{36}\end{array}$            

Observing the adjacent sides  $AB,BC$are equal, and the lengths of the diagonal are equal

Diagonals are equal, and adjacent sides are equal 

Therefore, the quadrilateral formed by the given vertices is square.