The radius of a hydrogen-like ion is calculated using the formula:\[r = r_0 \frac{n^2}{z}\]Here, \( r_0 \) represents the radius of hydrogen, \( n \) is the principal quantum number, and \( z \) is the atomic number. For the ion \( \text{Li}^{2+} \), with \( n = 1 \) and \( z = 3 \), the radius is determined as follows:\[r = r_0 \frac{1^2}{3} = \frac{r_0}{3}\]Therefore, \( X = 3 \).