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.
Current limitations: 1  An IRA can only be funded with cash or cash equivalents. 2  Additionally, an IRA (or any other tax-advantaged retirement plan) can only be funded with what the IRS calls taxable compensation. 3  Rollovers, transfers, and conversions between IRAs and other retirement arrangements can include any asset.