Final answer:
Rockefeller's heirs did not have to hand over 70% of their inherited property to the federal government; this statement is false. Tax rates on estates have varied, and Rockefeller's philanthropic efforts and established trusts would have influenced the taxable amount of his estate.
Step-by-step explanation:
The claim that Rockefeller's heirs had to hand over 70% of their inherited property to the federal government upon his death is false. At the time of Rockefeller's death in 1937, estate taxes were indeed quite high, but not as much as 70% for the entirety of the estate. The actual rate would have varied depending upon the value of the estate and the tax laws in effect at the time. Additionally, Rockefeller had established several trusts and had given away much of his wealth to philanthropic causes, which would have significantly affected the taxable portion of his estate. The tax rate itself has varied over time, particularly during the 20th century, with significant changes depending on legislative reforms and policy shifts.