"which country in australia and oceania is one of the world's most densely populated? "

Tuvalu

Explanation:

it is a country located in Polynesia located with shores of the Pacific Ocean

Tuvalu

Explanation:

Tuvalu, in the South Pacific, is an independent island nation within the British Commonwealth. Its 9 islands comprise small, thinly populated atolls and reef islands with palm-fringed beaches and WWII sites. Off Funafuti, the capital, the Funafuti Conservation Area offers calm waters for diving and snorkeling among sea turtles and tropical fish, plus several uninhabited islets sheltering sea birds.

Tuvalu is a group of nine tiny islands in the South Pacific that won independence from the United Kingdom in 1978. Formerly known as the Ellice Islands, all are low-lying, with no point on Tuvalu being higher than 4.5m above sea level.

answer at the divergent plate boundary in the middle of the ocean;