If linear DNA has no recognition site how many fragments will be obtained after restriction enzyme treatment?

Correct answer: One uncut fragment

A restriction enzyme can cut DNA only when its particular recognition sequence is present. If a linear DNA molecule contains no such site, the enzyme has no suitable location to bind and cleave. Consequently, the DNA molecule remains intact under the stated treatment. Because the molecule is linear and is not cut, it is counted as one continuous DNA fragment. This conclusion assumes the enzyme is active and the conditions are suitable, as the question intends.

Therefore option A, one uncut fragment, is correct. Two fragments would require one cut in a linear molecule, while three or four fragments would require still more cuts. Since the question states that there is no recognition site at all, none of those cuts can occur. The original DNA does not disappear; it remains as a single fragment of its original length.