The HSN (Harmonised System of Nomenclature) code for sunglasses is 9004. This heading includes spectacles, goggles and other similar articles, corrective, protective or other.
Here is a description:
90: Optical, photographic, cinematographic, measuring, checking, precision, medical or surgical apparatus and instruments; their parts and accessories
04: Spectacles, goggles and other similar articles; corrective, protective or other
Specifically, sunglasses can be classified as:
9004.10: Sunglasses
For GST purposes in India, the GST rate for items classified under HSN code 9004.10 is generally 18%.