Which of the following words is closest in meaning to “Nonchalance”?

Nonchalance means a casual lack of concern.

• Correct answer - unconcern: it has the same meaning as Nonchalance.
• earnest endeavour: a sincere effort - wrong, it does not mean the same as Nonchalance.
• non-classified: not secret - wrong, it does not mean the same as Nonchalance.
• attentiveness: careful attention - wrong, it does not mean the same as Nonchalance.