In the context of any country, which one of the following would be considered as part of its social capital?

Social capital refers to the networks of relationships among people in a society that enable that society to function effectively. It includes features of social organization such as networks, norms, and social trust that facilitate coordination and cooperation for mutual benefit.

Let's examine the options:

A) The proportion of literates in the population: This is a measure of human capital, which refers to the skills, knowledge, and experience possessed by an individual or population. B) The stock of its buildings, other infrastructure and machines: This refers to physical capital, which includes tangible assets used in production. C) The size of population in the working age group: This relates to demographic structure and potential labor force, which is part of human capital or demographic dividend. D) The level of mutual trust and harmony in the society: This directly embodies the core elements of social capital – the intangible assets derived from social connections, shared norms, and trust that enable collective action and societal cohesion. Therefore, the level of mutual trust and harmony in the society is the most appropriate definition of social capital among the given options.