I Think it is Carbon Monoxide Because of the Following Reasons :
[tex]\clubsuit[/tex] From the Picture, We can Notice that the Both Atoms are Approximately of Same Size or Diameter. Carbon and Oxygen have Approximately Same Diameter.
[tex]\clubsuit[/tex] It Cannot be Nitrogen, Because the Color of Atoms is Different. So, They must be of Different Element's Atoms.
[tex]\clubsuit[/tex] It Cannot be Krypton, Because Krypton is a Noble Gas it does not Pair up with other Atoms.
[tex]\clubsuit[/tex] It Cannot be Hydrogen Chloride, Because There is a Big Difference between the Size of Hydrogen and Chlorine Atom.
[tex]\clubsuit[/tex] It Cannot be Sulphur dioxide, Because Sulphur dioxide Contains 3 Atoms. One Sulphur and Two Oxygen Atoms.
