When tolerance is given on one side of the basic dimension, it is called:

Correct option is B

Unilateral tolerance allows variation in one direction only (either above or below the basic size). In bilateral tolerance, variations are allowed in both directions. Tolerance: Acceptable dimensional variation from the nominal size.
Allowance: Intentional difference for proper fit.
Unilateral Tolerance: e.g., +0.00, -0.02 mm.
Bilateral Tolerance: e.g., ±0.02 mm.