Answer is: a single atom of chlorine.
Chlorine has electron configuration: ₁₇Cl 1s²2s²2p⁶3s²3p⁵.
According to his electron configuration, chlorine needs one electron to achive noble gas configuration (most stable because <span>valence shell is filled).
NaCl, H</span>₂O and Ar have stable electron configuration.
I’m almost 100% sure it’s D
