Defence is part of  A. Export index  B. Stock Market Index  C. Hard Power Index  D. Welfare Index

To determine which of the options listed relates to "defence," let's analyze each choice:

1. Export Index: This index typically measures a country's export performance in various sectors, and it does not directly relate to defence.

2. Stock Market Index: This reflects the performance of a group of stocks and is primarily focused on financial markets, which again does not directly tie to defence.

3. Hard Power Index: Hard power refers to a country's ability to use military force or economic coercion. This index would be directly related to defence capabilities and military strength.

4. Welfare Index: This index assesses the well-being and quality of life of a population, which does not encompass defence.

Conclusion

Based on the analysis, the correct answer is C. Hard Power Index, as it directly pertains to a nation’s military capabilities and defence mechanisms.