yes, ask at a bike shop or in touristed areas of recreational value
That would be dependent on local law, age/weight of additional rider and type of bike. Many places forbids an adult to carry another adult on the rack of a bike, while tandems and carrying kids are OK.
A spinning bike, a stationary bike or an exercise bike.
An adult monkey is called an adult monkey
Typically the size of a chain on an adult bike should be one 16th of an inch or less. It is recommended to replace the chain on your bike if it exceeds one 16th of an inch.
the things on both sids of each tire on a trick bike or bmx bike are called pegs
Hatchling -> baby -> juvi -> adult. An adult leopard gecko would be called an adult.
The adult seahorse is called seahorse.
An adult zebra is called a zebra.
An adult rat is called a rat.
An adult jellyfish is called a Jellyfish.
Depending on the bike yes most adult sized bikes have gears