The correct answer is option 3, Sucralose. Sucralose is an artificial sweetener that is derived from sugar. It is made by modifying the structure of sugar molecules through a process that replaces three hydrogen-oxygen groups with chlorine atoms. This modification makes sucralose much sweeter than sugar but with significantly fewer calories.

Now let`s analyze the other options to better understand them:

- Option 1, Aspartame, is not modified sugar. It is made by combining two amino acids, aspartic acid and phenylalanine.

- Option 2, Saccharin, is also not modified sugar. It is a compound derived from the oxidation of a natural compound called o-toluene sulfonamide.

- Option 4, Alitame, is an artificial sweetener but it is not modified sugar either. It is a peptide-based sweetener made from aspartic acid and alanine.

In summary, while options 1, 2, and 4 are artificial sweeteners, only option 3, Sucralose, is actually modified sugar.