The correct answer is "unos relojes nuevos" because it is the plural form of "un reloj nuevo." In Spanish, when referring to more than one item, the indefinite article "un" changes to "unos" and the noun "reloj" also changes to its plural form "relojes." Additionally, the adjective "nuevo" agrees in number and gender with the noun it modifies, so it changes to "nuevos" to match the plural noun "relojes."