Can leadership claim (ex: No. 1) of a product be made in an advertisement?

No, the use of leadership claim of a product is prohibited. Surveys relying on unvalidated data, due to a lack of recognition by authorities, may deem the claims unjustifiable. Furthermore, making a leadership claim of a product in another way tends to disparage and discredit competitor’s product directly or by implication. Please refer to Registered Medicinal Product Advertising Approval Guidelines Paragraph 3.9 Denigration, Refution And Disparagement Towards Other Parties and Appendix 7 No. 19 (List of Superlatives/Hyperboles).