**Core Concept**
The Poison's ratio, also known as the Poisson's ratio, is a fundamental property of materials that describes the lateral strain or deformation of a material in response to a longitudinal tensile loading. It is an important parameter in the design and analysis of biomedical devices, implants, and other medical equipment.

**Why the Correct Answer is Right**
The value of the Poison's ratio for an ideal isotropic material is 0.5. This means that when an ideal material is subjected to a tensile force in one direction, it will deform by 0.5 times the amount of the applied force in the direction perpendicular to the applied force. This is because an ideal isotropic material has the same elastic properties in all directions. The value of 0.5 is a characteristic of a perfectly elastic material that returns to its original shape after the applied force is removed.

**Why Each Wrong Option is Incorrect**
**Option A:** This value is not applicable for an ideal isotropic material, as it would not be able to deform in response to an applied force.
**Option B:** This value is too low, as it would indicate a material that is too rigid and unable to deform under tensile loading.
**Option C:** This value is too high, as it would indicate a material that is too compliant and would not return to its original shape after the applied force is removed.

**Clinical Pearl / High-Yield Fact**
The Poison's ratio is an important property of materials in medical devices, as it affects the performance and durability of the device. A material with a high Poison's ratio may be more prone to deformation and failure under tensile loading.

**Correct Answer:** . 0.5