D, <span>Monotonic gases, which have no inter molecular attractions are most suited as ideal gases </span><span />
NO₂ is a brown gas while N₂O₄ is colorless. If heating causes a brown color to persist, then this means that heating causes the reaction to shift backwards and produce NO₂. Therefore, the reaction must be exothermic.
Answer:7 atom of carbon+5atom of hydrogen +3atom of nitrogen +6 atom of oxygen =21
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