What is the most populous country in Oceania?

Which country has the third-largest population in Southeast Asia? What is the most populous country in South Asia, excluding India? Which country is the second most populous in East Asia? What is the most populous country in South Asia? Which country has the third-largest population in South America? What is the second most populous country in Southeast Asia? Which country is the most populous in West Africa? Which is the third most populous country in the world?