Q.________ is the main investor in small scale industry.

The private sector — individual entrepreneurs and private investors — is the main source of investment in small-scale industry, option (b).

Small-scale industries (SSIs) in India are, by their very nature, typically small, individually or privately owned and financed enterprises — sole proprietorships, partnerships, or small private companies — set up with the personal savings of entrepreneurs, family contributions, and borrowed funds from banks/financial institutions (like SIDBI). The government does support SSIs through policies, subsidies, and reserved sectors, but it is private individuals/entrepreneurs who actually invest their own capital and bear the risk of running these units — not the government, which does not typically own small-scale units directly.

The other options do not fit: …