The HNO3 molecule, which is also known as nitric acid, consists of one hydrogen atom (H), one nitrogen atom (N), and three oxygen atoms (O). In its gaseous state, HNO3 adopts a planar shape.

Explanation:
- HNO3 contains a central nitrogen atom (N) surrounded by three oxygen atoms (O) and one hydrogen atom (H).
- The nitrogen atom has five valence electrons, while each oxygen atom has six valence electrons. The hydrogen atom contributes one valence electron.
- In order to determine the shape of the molecule, we need to consider the arrangement of the atoms and the number of electron pairs around the central atom.
- The nitrogen atom in HNO3 is sp2 hybridized, which means it forms three sigma bonds with three oxygen atoms.
- The oxygen atoms are also sp2 hybridized and form sigma bonds with the nitrogen atom.
- The hydrogen atom is attached to one of the oxygen atoms through a sigma bond.
- The electron pair geometry around the nitrogen atom is trigonal planar, as it has three regions of electron density (three sigma bonds).
- The molecular geometry, also known as the shape, is determined by considering the electron pairs and the atoms bonded to the central atom.
- In this case, the molecular geometry is also planar, as all the atoms and electron pairs are in the same plane.
- Thus, the HNO3 molecule in its gaseous state adopts a planar shape.
- The planar shape of HNO3 can be visualized as a flat molecule with the nitrogen atom at the center and the three oxygen atoms and one hydrogen atom arranged in a flat plane around it.