A known artificial sweetener X is composed of 4-chloro-4-deoxy-α-D-galactose and 1,6-dichloro-1,6-dideoxy-β-D-fructose joined by a glycosidic linkage.

Structure of D-galactose is given below:

The correct option is D.

To identify the correct chemical structure of the artificial sweetener Sucralose (labeled as artificial sweetener X), let us break down the components and stereochemistry specified in the question:

1. Structure of 4-chloro-4-deoxy-α-D-galactose unit:

From the Fischer projection of D-galactose provided in the image:
- Standard D-galactose has configuration at C4 with -OH on the left.
- In Haworth projection / chair representation, for an α-D-galactopyranose derivative:
• At C1 (anomeric carbon), the α-anomer has the hydroxyl (-OH) group pointing downwards (trans to C5 -CH₂OH group). Therefore, the glycosidic linkage starts from C1 pointing downwards.
• At C4, inversion of configuration occurs when chlorine replaces the -OH group, or we verify its orientation carefully. In 4-chloro-4-deoxy-α-D-galactose (which is derived from sucrose/sucralose configuration), chlorine (-Cl) at C4 is positioned such that -Cl is wedged/pointing up or in the configuration shown correctly in option D.

2. Structure of 1,6-dichloro-1,6-dideoxy-β-D-fructose unit:

For β-D-fructofuranose derivative:
- At C2 (anomeric carbon of fructose), the β-anomer means the oxygen linkage is formed at C2, with the -CH₂Cl group at C1 positioned in the correct relative orientation.
- At C6, the hydroxyl group is replaced by chlorine (-CH₂Cl).

3. Glycosidic Linkage:

The glycosidic bond connects C1 of the α-D-galactose unit to C2 of the β-D-fructose unit (specifically an α-1,2'-glycosidic linkage, as seen in sucrose analogs like Sucralose).

4. Comparing the given options:

Looking at the structural representations in the provided image:

- In Option D:
• The galactose ring has the α-configuration at C1 connecting downwards to C2 of the fructofuranose ring.
• The positions of the chlorine (-Cl) atoms at C4 of galactose, and at C1 (-CH₂Cl) and C6 (-CH₂Cl) of fructose perfectly match the structural formulas of Sucralose.

Therefore, Option D represents the correct chemical structure of sweetener X.