The correct answer is option 'D' - All (i), (ii), and (iii).

Explanation:
Micro-teaching is a teacher training technique that involves breaking down the teaching process into small, manageable parts. It allows teachers to practice and refine their teaching skills in a controlled and supportive environment. In the context of mathematics, micro-teaching focuses on developing specific skills related to teaching mathematics effectively. Let's discuss each of the given skills in detail:

i. The skill of integrating knowledge and experience:
- Integrating knowledge and experience refers to the ability to connect theoretical concepts with real-life experiences.
- In the context of mathematics, it involves linking mathematical concepts with practical examples, applications, and real-world problems.
- This skill helps teachers make the subject more relatable and meaningful for students, enhancing their understanding and engagement.

ii. The skill of facilitating child-centric learning:
- Facilitating child-centric learning refers to creating a learning environment that is student-centered, where students are active participants in their own learning process.
- In the context of mathematics, teachers with this skill focus on promoting student engagement, critical thinking, problem-solving, and collaborative learning.
- They encourage students to explore different strategies, ask questions, and make connections, fostering a deeper understanding of mathematical concepts.

iii. The skill of developing observation in learners:
- Developing observation in learners involves helping students develop their observational skills and abilities to analyze and interpret information.
- In the context of mathematics, this skill enables students to carefully observe patterns, relationships, and structures within mathematical concepts.
- It enhances their ability to make connections, identify patterns, and develop mathematical reasoning and problem-solving skills.

The given options state that all three skills are part of micro-teaching in mathematics. Therefore, the correct answer is option 'D' - All (i), (ii), and (iii).

To summarize:
- Micro-teaching in mathematics involves integrating knowledge and experience, facilitating child-centric learning, and developing observation skills in learners.
- These skills contribute to effective teaching and learning of mathematics by making the subject more meaningful, engaging, and accessible to students.