Good bikes are made in different frame sizes. And dedicated riders often chainge the gearing ratio by replacing either the sprocket or the driver with one with another tooth count than it came with.
These things influence chain length, so you see that no one can tell how many links your chain should be.
Chains are just about Always bought a Little long, then cut to length on the bike. Faster than counting links. Chain breakers aren't expensive. Either have a shop fit the chain when you buy it, or get a chain breaker (and a quicklink) and fit it yourself.
Do note that chain, driver and sprocket wear together, but usually the chain wears the fastest.
So sticking a new chain on old sprockets can often lead to the chain skipping and slipping.
If you don't know how to measure a chain for wear, better replace aat least chain and driver at the same time.
Both Mongoose and Schwinn make a wide range of bikes. It's not possible to tell which brand is best w/o knowing which model you are thinking about.
27 cm (2009 model)
Google can't find one.
The manual, if available, can be found at the links below. The parts link will tell you if the manual is at Manage My Home and link to it.
it appends on the bikes model
There are 4 CVO bikes in 2009.
on the frame close to the handdle bars there will be a sticker that tells you year make and model
Mercier has released many different models of bikes. Some of their bike model names include Shimano Equipped Steel, Shimano Equipped Aluminum, and Campagnolo Equipped Steel.
Chain.
It has a chain.
You can buy exercise bikes that specifically cater to spinning. The model should have the information right on the box but if not, ask the store sales associate for help.
Sorta, hard to answer as you listed no model.