Step 1: Statement (I) is correct. Lassaigne's test is used to detect the presence of nitrogen, sulfur, halogens, and phosphorus in an organic compound by fusing it with sodium metal to form sodium salts of these elements.
Step 2: Statement (II) is also correct. In Lassaigne's test, the elements are converted into their ionic forms by fusing the organic compound with sodium or magnesium. This makes it easier to test for the presence of elements like nitrogen, sulfur, and halogens.
Thus, the correct answer is that both Statement I and Statement II are true.