Step 1: Concept
A triangle is right-angled if one of its interior angles is $90^{\circ}$.
Step 2: Analysis of Statement I
The angles are given as $30^{\circ}$, $60^{\circ}$, and $90^{\circ}$. Since one angle is $90^{\circ}$, it is definitively a right-angled triangle. Statement I alone is sufficient.
Step 3: Analysis of Statement II
Knowing the longest side is 10 units does not determine the angles of the triangle. Not sufficient.
Step 4: Conclusion
Statement I alone is sufficient, so the answer is (1).
Final Answer: (1)