Answer and explanation:
To draw the Lewis structure we have to make sure that each element in the molecule has 8 electrons (Octet rule) in the valence shell, or 2 electrons in the hydrogen atom.
• PCl3:
In the PCl3 molecule, each chlorine atom has an Octet with 8 electrons, and the phosphorus atom also has an Octet but it is expanded (that means, that P atomd can have more that 8 electrons). From period 3 of the Periodic Table, elements can expand their octet and have more than 8 electrons.
• H2O2:
In the H2O2 molecule, oxygen atoms have an Octet with 8 electrons and hydrogen atoms have an Octet with 2 electrons.
• CH2Cl2:
In the CH2Cl2 molecule, all atoms have octets with 8 electrons, except for hydrogen, which has an octet with 2 electrons.
• H2CO2:
In this case, the Octet rule is fulfilled and also for this, an oxygen atom must form a double bond with the chlorine atom.