Step 1: Understand the role of the UN Secretary-General.
The Secretary-General is the chief administrative officer of the United Nations and head of the UN Secretariat. They are appointed for a five-year term, which can be renewed.
Step 2: Identify the current Secretary-General and their number.
The current and 9\textsuperscript{th} Secretary-General is António Guterres. He is a Portuguese politician and diplomat who took office on January 1, 2017. He was re-appointed for a second term that began in 2022.
Step 3: Identify the other individuals listed.
(L) Ban Ki-moon (South Korea) was the 8th Secretary-General, serving immediately before Guterres (2007-2016).
(M) Kofi Annan (Ghana) was the 7th Secretary-General (1997-2006).
(N) Justin Trudeau is the Prime Minister of Canada, not a UN Secretary-General.
Therefore, António Guterres is the correct 9th Secretary-General.