Final answer:
The colorless gas that decomposes to produce equal volumes of N₂ and half the volume of O₂ at STP would likely be dinitrogen tetroxide (N₂O₄), which is not listed among the options.
Step-by-step explanation:
The question asks to identify a colorless gas that decomposed to give equal volumes of N₂ (nitrogen) and half that volume of O₂ (oxygen) at standard temperature and pressure (STP). Since all gases at STP have the same molar volume due to Avogadro's law, we can infer that the decomposition of the original gas produced equal moles of N₂ and half as many moles of O₂.
The only gas among the choices provided, which decomposes into these two gases in such a mole ratio, is dinitrogen tetroxide (N₂O₄), which is not one of the options listed but is known to be a colorless gas that decomposes into N₂ and O₂. However, if we assume one of the options is meant to be N₂O₄, then the answer would indeed be this unlisted gas: Dinitrogen Tetroxide (N₂O₄), not H₂ (hydrogen), He (helium), Ne (neon), or Ar (argon), since these gases do not decompose into nitrogen and oxygen.
Therefore, the options provided are incorrect.