Fructose is a monosaccharide with the molecular formula C\(_6\)H\(_{12}\)O\(_6\). When represented by the general formula C\(_x\)(H2O)\(_y\), it can be written as C\(_6\)(H\(_2\)O)\(_6\). Therefore, the value for "X" (the number of carbon atoms) is 6.

A. 3 is incorrect because a 3-carbon sugar (triose) like glyceraldehyde has the formula C\(_3\)H\(_6\)O\(_3\), which is not fructose.

B. 12 is incorrect because 12 carbons indicates a disaccharide (like sucrose,C\(_{12}\)H\(_{22}\)O\(_{11}\)) or a polysaccharide, not a single fructose molecule.

C. 5 is incorrect because a 5-carbon sugar (pentose) like ribose has the formula C\(_5\)H\(_{10}\)O\(_5\), which is not fructose.

The correct answer is option D.