The chronological order of the approaches of human geography is:

(2) (C), (D), (B), (A)

Explanation:

• (C) Areal differentiation: This approach, focusing on regional variations and spatial patterns, is an early perspective in human geography.
• (D) Spatial Organisation: This approach involves the study of how human activities are organized and distributed in space.
• (B) Behavioural school: This approach, emphasizing human behavior and psychological factors, gained prominence in the mid-20th century.
• (A) Postmodernism: This is a more recent approach that challenges traditional theories and emphasizes the complexity of contemporary societies.