Answer
The statement is true.
Work Step by Step
As we have just shown in part (a), cations are smaller than their corresponding neutral atoms. The reason is that while the nuclear charge remains unchanged, the fewer number of electrons in cations means there is less electron-electron repulsion, making the electrons more attracted and be closer to the nucleus.
$Li^+$ is the cation of the neutral $Li$ as 1 electron has been removed. Since cations have smaller size than their corresponding neutral atoms, $Li^+$ is smaller than $Li$.
The statement is true.
