Final answer:
Adaptability and change management is the key management skill necessary for the 21st century.
Step-by-step explanation:
The key management skill necessary for the 21st century is Adaptability and change management. In today's fast-paced and constantly evolving business environment, organizations need leaders who can successfully navigate change and adapt to new circumstances. This skill involves being open to new ideas, being able to quickly adjust strategies and plans, and effectively managing and leading others through change.