Final answer:
The statement is false. The 26th Amendment, passed in 1971, lowered the voting age to 18 for both federal and state elections, following a Supreme Court ruling that Congress could only set the voting age for federal elections.
Step-by-step explanation:
The statement "When the Voting Rights Act of 1970 extended the right of eighteen-year-olds to vote in state elections, the Supreme Court declared the law unconstitutional" is false.
In fact, while the Voting Rights Act of 1970 did include a provision to lower the voting age to 18, the Supreme Court ruled that Congress could only set the voting age for federal elections, not for state or local elections.
This discrepancy prompted the passage of the 26th Amendment in 1971, which established the right of citizens 18 years of age or older to vote in federal and state elections, thus avoiding the need for separate voting rolls and ensuring a uniform voting age across the United States.