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A Lewis structure can be defined as the basic structure of a molecule which used the valence electron of each atom involved. In Lewis’s structure, the least electronegative atom will be the central atom.

In this molecule, the phosphorus has 5 electrons in the valence orbital which can bond to the 3 F-atoms and form three single bonds. There are remaining two electrons on P-atom which form a lone pair around the molecule and one electron is given by all 3 F-atom in order to fulfil the octet of each other.

${\mathbf{PF}}_3$is a Tetrahedral structure.

C belongs the group 14 having 4 electrons in the valence shell and requires 4 electrons, O-atom belongs togroup 16 having 6 electrons in the valence shell and requires 2 electrons to fulfil the octet and H belongs to group 1 having 1 electron in the valence shell requires 1 electron to fulfil the duplet. The 2 electrons required will be provided by 2 H to O-atom and 4 electrons from other 3 O-atom.

${\mathrm{H}}_2{\mathrm{CO}}_3$is Trigonal Planar.

In this molecule, the C-atom has 4 electrons in the valence orbital and requires 4 more electrons to fulfil the octet which is given by the S-atom and forms an unsaturated molecule having a double bond. The S-atom also require 2 electrons to fulfil its octet which is given by the C-atom.

${\mathrm{CS}}_2$is a Linear structure.