Does a Vauxhall corsa 2004 have belts or chains?

If referring to the Camshaft drive, it will depend on what engine the vehicle has.

Generally speaking 1.0 and 1.2 petrol engines and 1.3 diesel engines are chain driven.

1.4 may be chain or belt, depending on the exact 1.4 engine fitted.

The rest are belt driven.

to an experienced person it's easy to tell just by looking at the engine, as most belt driven engines have plastic cam-belt covers for easy access when replacing the belt every 40k miles, while a chain is built into the engine as it is not normally expected to need replacement, and so has in effect "metal covers" that are part of the engine, rather than separate covers.

If in doubt phone any Vauxhall/Opel dealer, ask for service, quote your registration or chassis number, and ask how much it will cost to replace your cam-belt. If is has a chain they will say so.

Expect to pay about £250-300 to replace a belt, and £600-1000 to replace the chain.