Explanation:

Introduction:
Radiation shape factor, also known as view factor or configuration factor, is a dimensionless quantity that represents the fraction of radiation leaving one surface that reaches another surface. It depends on the geometry and orientation of the surfaces involved.

Factors Affecting Radiation Shape Factor:
The value of the radiation shape factor depends on the relative position and size of the surfaces. The following factors affect the radiation shape factor:

1. Distance between Surfaces:
When the surfaces are closer together, the radiation shape factor tends to be higher. This is because a larger fraction of the radiation emitted by one surface can reach the other surface when they are in close proximity. Conversely, when the surfaces are further apart, the radiation shape factor tends to be lower because a smaller fraction of the radiation can reach the other surface.

2. Size of Surfaces:
The size of the surfaces also affects the radiation shape factor. Larger surfaces have a higher probability of intercepting radiation from other surfaces, leading to a higher radiation shape factor. Smaller surfaces, on the other hand, have a lower probability of intercepting radiation, resulting in a lower radiation shape factor.

3. Orientation of Surfaces:
The orientation of the surfaces relative to each other also influences the radiation shape factor. Surfaces that are facing each other directly have a higher radiation shape factor compared to surfaces that are angled or not facing each other directly. This is because the direct line of sight between the surfaces allows for a larger fraction of radiation to be exchanged.

Explanation of the Correct Answer:
Based on the given options, the correct answer is option 'B': Surfaces are larger and held closer. This means that when the surfaces are both larger in size and held closer together, the radiation shape factor will be higher.

This is because larger surfaces have a higher probability of intercepting radiation from each other, increasing the fraction of radiation that can be exchanged. Additionally, when the surfaces are held closer together, a larger fraction of the radiation emitted by one surface can reach the other surface, further increasing the radiation shape factor.

Therefore, option 'B' is the correct answer as it correctly identifies the conditions (larger surfaces held closer) that result in a higher radiation shape factor.