**Explanation:**

**Cast Iron**

Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%. It is widely used in various engineering applications due to its excellent castability, high wear resistance, and good thermal conductivity. However, cast iron components are susceptible to failure under certain conditions.

**Failure Criterion for Cast Iron Components**

The failure criterion for cast iron components refers to the condition at which the component cannot sustain any further load and breaks. In the case of cast iron, the ultimate tensile strength is considered to be the failure criterion. Let's understand why:

1. **Ultimate Tensile Strength (UTS):** The ultimate tensile strength is the maximum stress that a material can withstand before it breaks. It is determined by conducting a tensile test on a sample of the material. The UTS is an important parameter to determine the strength of a material and its ability to withstand loads.

2. **Yield Strength:** The yield strength is the stress at which a material begins to deform plastically, i.e., it undergoes permanent deformation without rupture. However, cast iron does not exhibit a well-defined yield point, as it undergoes gradual plastic deformation without a distinct yield strength. Therefore, the yield strength is not considered as the failure criterion for cast iron components.

3. **Endurance Limit:** The endurance limit, also known as the fatigue limit, is the maximum stress amplitude that a material can withstand for an infinite number of cycles without failing. It is a critical parameter for components subjected to cyclic loading. However, cast iron is not known for its high fatigue strength, and its endurance limit is relatively low compared to other materials. Therefore, the endurance limit is not considered as the failure criterion for cast iron components.

4. **None of the Mentioned:** Since the ultimate tensile strength is the maximum stress that a cast iron component can withstand before it breaks, it is considered as the failure criterion for cast iron components. Therefore, option 'A' is the correct answer.

In conclusion, the ultimate tensile strength is considered as the failure criterion for cast iron components. This parameter determines the maximum stress that the cast iron can withstand before it fractures and is used to assess the strength of cast iron components in engineering applications.