Which element from following has smallest ionic size in +3 state?

The ionic size of lanthanide $\text{M}^{3+}$ ions decreases steadily across the lanthanide series due to lanthanide contraction.
Of the given elements—lanthanum ($Z = 57$), neodymium ($Z = 60$), dysprosium ($Z = 66$), and lutetium ($Z = 71$)—lutetium has the highest atomic number and thus the smallest ionic radius.

$\text{Lu}^{3+}$ has the smallest ionic size.

The final answer is $\boxed{A}$.