Final answer:
The earliest-known name for Britain that was used around 300 B.C. is Albion, which is possibly derived from the Latin for 'white' in reference to the chalky White Cliffs of Dover. Other names like Britannia, Avalon, and Camelot have different origins and associations related to Roman Britain and Arthurian legend, respectively.
Step-by-step explanation:
The earliest-known name for Britain, likely referring to the White Cliffs of Dover, that was used around 300 B.C. is Albion. This name predates the Roman settlement in southern England and the subsequent invasions by the Anglo-Saxons. The name Albion is believed to derive from the Latin word 'albus' meaning white, which could be a reference to the striking white chalk cliffs along the southeastern coastline of Britain.
By contrast, Britannia was a term used by the Romans after their conquest and would come to personify the province of Roman Britain. Names like Avalon and Camelot are more associated with Arthurian legend rather than historical appellations for Britain. In summary, the term Albion is the most ancient name among the options given, which is tied to the geographical characteristic of the chalky cliffs of Dover. The Germanic tribes called the Anglo-Saxons eventually established the roots of what is now known as England, and their cultural identity became prominent long after the use of 'Albion'.