Step 1: Understand the question.
A dispute about the arbitral tribunal's own jurisdiction has come up. We must judge two statements under the Arbitration and Conciliation Act, 1996.
Step 2: Recall the key doctrine.
The idea of Kompetenz-Kompetenz means an arbitral tribunal can decide questions about its own power. Section 16 of the Act puts this idea into law to cut down court interference and speed things up.
Step 3: Test Statement I.
Statement I says the tribunal may rule on its own jurisdiction. Section 16(1) clearly allows the tribunal to rule on its own jurisdiction, including on whether the arbitration agreement exists or is valid. So Statement I is correct.
Step 4: Test Statement II.
Statement II says a plea that the tribunal lacks jurisdiction must be raised not later than the statement of defence, unless the tribunal allows a later plea. Section 16(2) says exactly this. The aim is to stop a party from joining the case and only later objecting to jurisdiction. So Statement II is correct.
Step 5: Combine the findings.
Both statements correctly reflect Section 16. So the right choice is the one saying both statements are true.
Step 6: Check the other options.
Options saying only one statement is true, or neither is true, are wrong because both match the section.
\[ \boxed{\text{Both Statements I and II are true}} \]