Air is mainly composed of nitrogen, oxygen, and argon, which together constitute the major gases of the atmosphere. Water vapor accounts for roughly 0.25% of the atmosphere by mass.
Physical property, such as real estate, does not qualify due to the unpredictable length of the sales process. As retirement accounts, 401(k)s and IRAs operate both as liquid assets and non-liquid assets depending on the circumstance.
Assets range in liquidity based on how hard they are to exchange for money. Items such as cash, gold or silver are considered highly liquid assets because they are exchanged relatively quickly with very little risk of loss. Land and housing are nonliquid assets, states AllBusiness, and it takes time and risk in order to exchange for higher-liquidity assets.