Explanation:

Here’s the thing—when you’re opening a demat account, some details are important, but one is absolutely non-negotiable in India. Let’s look at each option:

- Date of birth and address: Sure, both are pretty essential for identity checks and communication, but you could give these for a lot of financial services. Not unique to demat.

- PAN number: This is the real must-have. SEBI (the regulator) says no demat account without a PAN card, period. It’s how investors are tracked for compliance, tax, and everything else in the stock market.

- Residential status (Indian/NRI): Important, yes—it decides a lot about how you’ll invest. But still, the account can’t even start without the PAN.

- Bank account details: Also necessary for settlements and linking your demat, but here’s the bottom line: you can’t move ahead at all without the PAN.