Providing simple, concrete experiences to a mentally challenged child in the class is the most suitable strategy among the given options (C). This approach can effectively support their learning and development. Here's an explanation of why this strategy is the correct choice:

1. Individualized instruction:
- Mentally challenged children often require individualized instruction to meet their specific needs.
- By providing simple and concrete experiences, teachers can tailor their teaching methods to the child's learning style and abilities.

2. Concrete experiences:
- Mentally challenged children often struggle with abstract concepts and find it easier to understand and learn through concrete experiences.
- Concrete experiences involve hands-on activities, real-life examples, and visual aids that make learning more tangible and accessible for these children.

3. Enhancing comprehension:
- Complex and abstract concepts can be overwhelming for mentally challenged children, leading to difficulties in comprehension.
- By simplifying the content and presenting it in a concrete manner, teachers can help these children better understand and grasp the information being taught.

4. Engaging and motivating:
- Simple, concrete experiences can make learning more engaging and motivating for mentally challenged children.
- Hands-on activities and real-life examples capture their interest and help maintain their attention, making the learning process more enjoyable and effective.

5. Building foundational skills:
- Mentally challenged children often require additional support in building foundational skills, such as reading, writing, and basic math.
- By providing simple, concrete experiences, teachers can focus on developing these fundamental skills at an appropriate pace for the child.

6. Inclusive education:
- Inclusion is a crucial aspect of education, promoting equal opportunities and access for all students, including those with disabilities.
- Sending the child to a special school (option A) may segregate them from their peers and limit their social and emotional development.

In conclusion, providing mentally challenged children with simple, concrete experiences is the most effective strategy as it caters to their individual needs, enhances comprehension, promotes engagement, and builds foundational skills. It also aligns with the principles of inclusive education, ensuring that all students can learn and thrive together in a mainstream classroom setting.