Introduction:
In nucleate boiling, the pressure inside a bubble is higher than the pressure of the surrounding liquid. This phenomenon occurs when a liquid is heated to its boiling point and small bubbles of vapor form and rise to the surface. It is important to note that both the liquid and vapor are saturated, meaning they are at equilibrium at a specific temperature.

Explanation:
The correct answer to the question is option 'B' - the temperature of the liquid is lower than the temperature of the vapor. This can be explained by understanding the principles of phase change and the behavior of bubbles during nucleate boiling.

Boiling Point:
The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure. At this temperature, bubbles of vapor form within the liquid and rise to the surface. In the case of nucleate boiling, the pressure inside these bubbles is higher than the pressure of the surrounding liquid.

Pressure Difference:
The pressure inside a vapor bubble is determined by the temperature and the vapor pressure of the liquid. Since the liquid and vapor are saturated, the vapor pressure is constant at a given temperature. As the temperature increases, the vapor pressure also increases, leading to an increase in the pressure inside the bubbles.

Temperature Difference:
The temperature difference between the liquid and vapor can be understood by considering the heat transfer mechanisms involved in nucleate boiling. When the liquid is heated, energy is transferred to the bubbles, causing them to grow and rise. This transfer of energy can occur through conduction, convection, and radiation.

Heat Transfer:
During nucleate boiling, the liquid in contact with the surface is at a higher temperature than the bulk liquid. As the bubbles form and rise, they carry away heat from the surface, resulting in a cooling effect. This cooling effect lowers the temperature of the liquid in the vicinity of the bubbles.

Saturated Conditions:
In nucleate boiling, both the liquid and vapor are saturated, meaning they are at equilibrium at a specific temperature. The temperature of the liquid will always be lower than the temperature of the vapor because of the cooling effect caused by the heat transfer from the liquid to the bubbles.

Conclusion:
In summary, in nucleate boiling, the pressure inside a bubble is higher than the pressure of the surrounding liquid. Both the liquid and vapor are saturated, and as a result of heat transfer mechanisms, the temperature of the liquid is always lower than the temperature of the vapor. This understanding is crucial in various fields, including heat transfer and boiling heat transfer applications.