**Explanation:**

The correct answer is option **B** - Both A and R are individually true but R is NOT the correct explanation of A.

**Assertion (A):** Plastic deformation is a function of applied stress, temperature, and strain rate.

**Reason (R):** Plastic deformation is accompanied by a change in both the internal and external state of the material.

Let's analyze each statement separately:

**Assertion (A): Plastic deformation is a function of applied stress, temperature, and strain rate.**

Plastic deformation refers to a permanent change in shape or size of a material, which occurs when the material is subjected to stress beyond its elastic limit. The three factors mentioned, namely applied stress, temperature, and strain rate, play a significant role in determining the extent of plastic deformation.

- **Applied Stress:** The applied stress is the external force acting on the material per unit area. When the applied stress exceeds the yield strength of the material, plastic deformation occurs. Higher stress levels result in more significant plastic deformation.

- **Temperature:** Temperature affects the plastic deformation behavior of materials. At higher temperatures, materials tend to exhibit greater plasticity, meaning they are more prone to plastic deformation. This is because elevated temperatures allow for more atomic mobility, facilitating the movement of dislocations and allowing for greater plastic flow.

- **Strain Rate:** The strain rate is the rate at which a material is deformed. It represents the change in strain per unit time. Higher strain rates can lead to increased plastic deformation. This is because a higher strain rate results in a greater number of dislocations being generated and moving through the material, leading to more extensive plastic flow.

Therefore, plastic deformation is indeed a function of applied stress, temperature, and strain rate.

**Reason (R): Plastic deformation is accompanied by a change in both the internal and external state of the material.**

Plastic deformation involves the permanent rearrangement of atoms or molecules within a material, resulting in a change in shape or size. This rearrangement occurs at both the internal and external levels of the material.

- **Internal State:** Plastic deformation is associated with the movement of dislocations, which are line defects in the crystal lattice. These dislocations act as carriers of plastic flow, allowing the material to undergo plastic deformation. As dislocations move and interact, they create new stress fields and rearrange the internal structure of the material.

- **External State:** Plastic deformation is visible at the macroscopic level, where the material undergoes a change in shape or size. This change in the external state of the material is a result of the internal rearrangements occurring at the atomic or molecular level.

Therefore, it is true that plastic deformation is accompanied by a change in both the internal and external state of the material.

However, the reason provided does not explain why plastic deformation is a function of applied stress, temperature, and strain rate. It only describes the consequences of plastic deformation. Hence, the reason is **not the correct explanation of the assertion**.

In conclusion, both Assertion (A) and Reason (R) are individually true, but Reason (R) is NOT the correct explanation of Assertion (A).

Statement (I) : Parts made by powder metallurgy do not have as good physicalproperties as parts casted.
Statement (II) : Particle shape in powder metallurgy influences the flowcharacteristic of the powder