You first have to compare GDP, all the ranks have their GDP and for China to be placed at the position that it is that's because it doesn't stand within the GDP of a developed country.
Since many years ago, China has the second largest nominal GDP and it is far higher than the third highest. If it is the PPP, China is the highest in the world.
Iran having 20% of oil passage route doesn't make them a developed country, Nigeria is in a big name in countries with crude oil as their natural resources but it is an under developed country, so a country can have the natural resources and have not made anything from it.
Nigeria is not an underdeveloped country, it is a developing country.
.what I actually meant is China has a low GDP per Capita, we have to recognize that it has the second largest population in the world just behind india.
On Nigeria it actually preferences, the world bank considers Nigeria a developing country, but since Nigerian indigenous news paper considered it under developed, realistically as a Nigerian I think we suffer some economic hardship that doesn't befit our status.