Justify
Definition
Support a decision or conclusion with reasons or evidence.
Explanation
You state your position, then give the evidence or reasoning that supports it, and may address alternatives.
Example
Justify your choice of sample size.
In an exam
Command-word meanings can vary between subjects, exam boards and mark schemes, so check your own board's guidance. See Exam Command Words: What Each Instruction Asks For.
Common confusion
Justify asks for support for a view, not a neutral summary.