Surfactant A shows a steeper slope than surfactant B in surface tension vs log concentration plots. What does steeper slope indicate?

a) Surface B has negative surface excess at the air liquid interface

b) Surfactant A adsorbs more than surfactant B at the air - liquid interface

c) Surfactant A adsorbs less than surfactant B

d) Surfactant A has negative surface excess at the air liquid interface