Final answer:
The best postmortem action to potentially minimize estate tax liability is the use of the alternate valuation date for estate assets, which might lower the taxable estate value due to decreased asset values after the date of death.
Step-by-step explanation:
The option that would likely help minimize estate tax liability for the deceased client's estate valued at $14 million is a) the use of the alternate valuation date for estate assets. Due to significant declines in the value of renovated apartments and slow growth in the limited partnership interests, the estate could benefit from the alternate valuation date if the value of the assets has decreased since the date of death. This postmortem action could result in a lesser valuation of the estate, thereby reducing the estate tax liability. It is important to note that in 2022, the estate tax applied only to estates exceeding $12.06 million, which means that this estate would indeed be subject to tax. The alternate valuation method may lower the taxable estate below the threshold or reduce the tax due, depending on the extent to which values have fallen.