Why does task manager show multiple chrome?

By default Google Chrome Web Browser opens each web site instance in separated process.

You can change it to different memory allocation model:

1. Process-per-site-instance
   It is default model.
2. Process-per-site
   Add --process-per-site option running chrome from the command line.
3. Process-per-tab
   Add --process-per-tab option running chrome from the command line.
4. Single process
   Add --single-process option running chrome from the command line.

From Chromium documentation:

Chromium supports four different models that affect how the browser allocates pages into renderer processes. By default, Chromium uses a separate OS process for each instance of a web site the user visits. However, users can specify command-line switches when starting Chromium to select one of the other architectures: one process for all instances of a web site, one process for each group of connected tabs, or everything in a single process. These models differ in whether they reflect the origin of the content, the relationships between tabs, or both. This section discusses each model in greater detail; caveats in Chromium's current implementation are described later in this document.

References

1. The Chromium Project -> Process Models