1) The longest English word is "pneumonoultramicroscopicsilicovolcanoconiosis," which refers to a lung disease caused by inhaling very fine silica dust.

2) International relations encompass the study of relationships between nations, including diplomacy, treaties, and foreign policy. It examines the interactions and dynamics among different countries in the global arena.

3) The word "pencil" contains two vowels: E and I.

4) The Victoria Falls, situated on the Zambezi River between Zambia and Zimbabwe, is one of the largest and most spectacular waterfalls in the world. It is over 1.7 kilometers (1 mile) wide and has a height of 108 meters (354 feet), attracting visitors with its breathtaking beauty and power.