ANS:B - one

The number of degrees of freedom for an azeotropic mixture in a two-component vapor-liquid equilibrium is zero. In a two-component system at equilibrium, the number of degrees of freedom is determined by the phase rule, which is given by: 𝐹=𝐶−𝑃+2F=C−P+2 Where:

• 𝐹F is the number of degrees of freedom,
• 𝐶C is the number of components (in this case, 2),
• 𝑃P is the number of phases.

For azeotropic mixtures, the composition of the vapor and liquid phases is fixed at equilibrium, meaning there is no freedom to change the composition without altering the conditions. Therefore, 𝑃=2P=2 (for two phases: vapor and liquid) and 𝐹=0F=0. So, the correct answer is zero.