Reddit reviews CHAIN 8SP KMC X8-Silver/Grey - X8.93

I believe lots of bikes were under the Technium label, from road bikes to mountain bikes.

Key point is how many cogs at the rear. At a guess, 7 or so, and most chains for >= 7 gears should work. KMC are good, and inexpensive.

However, if your chain broke, it's likely to mean that it was worn way past a reasonable max. A worn chain means worn cogs, and putting a fresh chain on worn cogs often means skipping. You may have to buy a new cassette/freewheel, and possibly new chainrings. Or find a source of partially worn chains to match your worn cogs.

https://www.sheldonbrown.com/chain-wear.html

The good news is that Shimano 7 speed is mostly compatible with 8 speed, so you can buy slightly more modern parts....

Claris 46/34t crankset, $35: https://www.amazon.com/dp/B00C45HO0I/

Claris FD-2400, $20: https://www.amazon.com/dp/B00CABQZQ0

Claris RD-2400 GS, $24: https://www.amazon.com/dp/B00CABM7XK/

KMC X8.93 Chain, $12: https://www.amazon.com/dp/B001MXQHPG/

Marlin 5 looks like a 7 speed. So pretty much any old chain will work fine.
https://www.amazon.com/KMC-X8-93-Bicycle-Chain-7-3mm/dp/B001MXQHPG/

*edit, this one is $2 cheaper.
https://www.amazon.com/KMC-Z-72-7-8sp-chain-Brown/dp/B001CN6QA2

New tires/tubes, new cables and repack the bearings/bottom bracket. Toss on a new chain too, that one looks a bit done - get a KMC 8 speed

After that you've essentially got yourself a brand new bike that will last you a long long time.

Also, here's new brake hoods since those hoods look like they're about to fall apart