The primary purpose of services in Angular is to handle HTTP requests and share data between different components. Services act as a central place to manage data and provide methods for components to interact with that data. While services can be used for other purposes like routing or storing configuration, their primary role is data management and communication between parts of an Angular application.

When creating a service in Angular using the Angular CLI, you would use the command ng generate service. This command generates the necessary files and boilerplate code for an Angular service, making it a convenient way to create services in an Angular project. The other options (ng serve, ng create service, ng build service) are not the correct commands for creating a service.

In Angular, the ngAfterViewInit lifecycle hook is most appropriate when you need to perform initialization logic after a component's views have been rendered. This hook is called once when the component's view and its children's views are initialized. ngOnInit is called earlier, before child views are ready, and the other options are not typically used for initialization logic in this context.

Angular's default change detection strategy checks components at predefined intervals. It periodically scans all components in the application for changes, which can be resource-intensive. This approach is less efficient than the OnPush strategy because it checks components even when no relevant changes have occurred. User interaction and asynchronous data arrival do not directly trigger checks in the default strategy.

In Angular, it's best to use the ngOnInit lifecycle hook to handle any additional initialization tasks, including making HTTP requests. The constructor is mainly used for dependency injection and not for logic.

In Angular's router, the pathMatch property is significant because it specifies how to match a URL path to a route. It has two values: 'prefix' (default) and 'full.' 'Prefix' means the route will match if the URL starts with the path, while 'full' requires an exact URL match. The other options do not accurately describe the purpose of pathMatch.

The *ngIf directive is used in Angular to conditionally add or remove an element from the DOM based on a given condition. If the condition evaluates to true, the element is rendered; otherwise, it is removed from the DOM. It's a fundamental directive for handling conditional rendering in Angular templates.

To ensure high performance with large datasets in Angular, developers should avoid data mutation and instead use immutable operations. Mutating data can lead to frequent change detection cycles and performance issues, as Angular may not detect changes in mutated objects. Using immutability ensures that each change results in a new object, making change detection more efficient.

To start the execution of an Observable and receive values from it, you need to call the subscribe method on the Observable instance. This method takes one or more callback functions to handle emitted values, errors, and completion.

In ViewEncapsulation.None mode, styles defined in the component can affect all elements in the application, and global styles can affect the component's elements. This mode effectively removes the shadow DOM boundary and makes the component's styles global. The other options describe the behavior of different encapsulation modes (such as ViewEncapsulation.Emulated, ViewEncapsulation.ShadowDom, and ViewEncapsulation.Native) but not the specific behavior of ViewEncapsulation.None.