Volume of a cone = 1/3 × πr²h. Here, volume = 1/3 × 3.14 × 12 × 12 × 68 = 10248.96 cubic mm. A cone has one circular base and tapers to a point, so its volume is one-third of a cylinder with the same radius and height. That is why the formula includes 1/3. The answer is in cubic units, so the correct choice is 10248.96 mm³.