Explanation:

In chemistry, the term planar geometry refers to a molecular geometry in which the atoms in a molecule lie on a single plane. This type of geometry is shown by molecules with sp2 hybridization.

The compound N(SiH3)3 has planar geometry. This is because the nitrogen atom in this compound has sp2 hybridization, which means that it has three hybrid orbitals that are involved in bonding with three SiH3 groups. These orbitals are arranged in a trigonal planar geometry around the nitrogen atom.

On the other hand, the compound N(t-Bu3) does not have planar geometry. This is because the nitrogen atom in this compound has sp3 hybridization, which means that it has four hybrid orbitals that are involved in bonding with three t-Bu groups and one hydrogen atom. These orbitals are arranged in a tetrahedral geometry around the nitrogen atom.

Similarly, the compounds NPh3 and NF3 do not have planar geometry. NPh3 has a pyramidal structure due to sp3 hybridization of the nitrogen atom, whereas NF3 has a trigonal pyramidal structure due to sp3 hybridization of the nitrogen atom.

Conclusion:

The compound N(SiH3)3 has planar geometry due to sp2 hybridization of the nitrogen atom, whereas N(t-Bu3), NPh3, and NF3 do not have planar geometry due to sp3 hybridization of the nitrogen atom.