The correct option is
B Surplus
The word 'deficit' refers to the amount by which something is too small.
Option A, surplus refers to an amount of something left over when requirements are met.
Option B, sufficiency refers to the condition or quality of being adequate or sufficient.
Option C, luxury refers to a state of great comfort or elegance, especially when involving great expense.
Option D, explicit refers to something stated clearly and in detail, leaving no room for confusion or doubt.
Thus, according to the meaning, the word 'surplus' is the most opposite in meaning from the word 'deficit'.