Hey 

First draw the Lewis dot structure:
Electron geometry: tetrahedral. Hybridization: sp3

Then draw the 3D molecular structure using VSEPR rules:

Decision:
The molecular geometry of SiH4 is tetrahedral with symmetric charge distribution around the central atom.
Therefore this molecule is non- planer

The molecular geometry of PCl5 is trigonal bipyramid with symmetric electron region distribution around the central atom.

 I Hope It Helps 

Good Luck