Extending an existing table such as the Task table when creating a new application has several benefits, such as:
You can repurpose existing fields by simply changing the label. For example, you can change the Short description field to Summary or Title for your new table.
You can use existing fields with no modifications. For example, you can use the Assigned to, Priority, and State fields for your new table without changing anything.
Existing logic from the parent table will be automatically applied to the new table. For example, you can inherit the Business Rules, Client Scripts, and UI Policies from the Task table for your new table.
The only option that is not true is d) All of the parent table records are copied to the new table. Extending a table does not copy any records from the parent table to the new table. It only creates a new table that inherits the fields and logic from the parent table.
References:
[Extend a table]
[Task table]

https://docs.servicenow.com/bundle/tokyo-servicenow-platform/page/administer/notification/task/t_CreateANoti
https://developer.servicenow.com/dev.do#!/learn/learning-plans/quebec/new_to_servicenow/app_store_learnv2_ The Weight field in an Email Notification determines which notification is sent when multiple notifications are triggered for the same record and recipients. Only the notification with the highest weight is sent. A weight value of zero means the notification is always sent when the notification's When to send criteria is met. A weight value of -1 means that no email should be sent3. References: Email Notification Weight

A Module Link type defines how the module opens in the content pane when the user clicks on it in the navigation pane1. The URL (from Arguments) link type allows you to specify a URL that opens the Application Properties page for the selected application2. The URL can include arguments that are evaluated at runtime, such as the application name or scope3.
Reference = 1: Module link types - ServiceNow Docs 2: Application properties - ServiceNow Docs 3: URL (from Arguments) - ServiceNow Docs

Explanation/Reference: https://hi.service-now.com/kb_view.do?sysparm_article=KB0716421

https://developer.servicenow.com/dev.do#!/learn/courses/tokyo/app_store_learnv2_scripting_tokyo_scripting_in_servicenow/app_store_learnv2_scripting_tokyo_server_side_scripting/app_store_learnv2_scripting_tokyo_script_includes