A Trivial Pursuit #15 (History 3/4): Those Not Present

Question

_{This is part 15 of A Trivial Pursuit, a 25-part puzzle hunt. Each part is solvable on its own, with the exception of the meta-puzzle at the end.}

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Eisenhower’s Vice President, later President himself	Norwegian composer of 'In the Hall of the Mountain King'	German aerial campaign against the UK in WWII, The _____	Lloyd Webber musical based on the life of the First Lady of Argentina	Island, home to the labyrinth of King Minos in Greek mythology
Sigmund, Austrian neurologist and father of psychoanalysis	House of five English monarchs, from 1485 to 1603	Spiro, 39th Vice President of the United States	Cleopatra, Maria Theresa, or Victoria?	Region of East Asia divided into two parts in the 1940s along the 38th parallel north
Ancient Greek philosopher, author of 'The Republic'	Birthplace of Marco Polo, Amerigo Vespucci, and Christopher Columbus	Biblical King, vanquisher of Goliath	Leader of the Israelites during their 40 years in the wilderness	Emperors of this country include Yoshihito, Hirohito, and Akihito
The first African-American President of the United States	Irish satirist and Anglican cleric, 'A Modest Proposal'	'Lion', 'Just' or 'Sun King'?	Exodus 3v8 description of the Promised Land: '…flowing with milk and _____'	Solve these clues to deduce the missing solution word, which has a connection to the formation of Pangaea

Note: If you find yourself thinking that there are multiple words that could fit the final clue in bold font, you probably haven't fully figured out the 'pattern' inherent in this puzzle just yet. Once you have the pattern nailed down in its entirety, it will become clear that there is only one possible answer...

Answer 1

The answer is

RHEIC "an ancient ocean which when closed formed Pangaea as a result" (thanks Beastly Gerbil)

The answers are

All five letter words with a notably pangramatic quality. There's also an acronym in the questions:

Eisenhower’s Vice President, later President himself - NIXON
Norwegian composer of 'In the Hall of the Mountain King' - GRIEG
German aerial campaign against the UK in WWII, The _____ - BLITZ
Lloyd Webber musical based on the life of the First Lady of Argentina - EVITA
Island, home to the labyrinth of King Minos in Greek mythology - CRETE
Sigmund, Austrian neurologist and father of psychoanalysis - FREUD
House of five English monarchs, from 1485 to 1603 - TUDOR
Spiro, 39th Vice President of the United States-AGNEW
Cleopatra, Maria Theresa, or Victoria?-QUEEN
Region of East Asia divided into two parts in the 1940s along the 38th parallel north - KOREA
Ancient Greek philosopher, author of 'The Republic' -PLATO
Birthplace of Marco Polo, Amerigo Vespucci, and Christopher Columbus - ITALY
Biblical King, vanquisher of Goliath - DAVID
Leader of the Israelites during their 40 years in the wilderness- MOSES
Emperors of this country include Yoshihito, Hirohito, and Akihito- JAPAN
The first African-American President of the United States - OBAMA
Irish satirist and Anglican cleric, 'A Modest Proposal' -SWIFT
'Lion', 'Just' or 'Sun King'? - LOUIS
Exodus 3v8 description of the Promised Land: '…flowing with milk and _____'-HONEY
(Solve these clues...)

The hidden acronym spells out ENGLISH SCRABBLE TILES.

We then note

Following the acronym clue, the English Scrabble set has 100 tiles including blanks. The above answers use 95 of these tiles including an A and a T as corresponding to blank tiles. This would leave the tiles CEHIR as 'those not present' (as per the title).

Furthermore

The answers begin with the letters A-T with the exception of R (thanks fljx) and so to fill that gap our answer must take the form R(CEHI*). Wikipedia then delivers us the Rheic Ocean.