To project content into multiple designated spots within a component's template in Angular, you would use multiple tags with select attributes. The select attribute allows you to specify which projected content should go where based on the content's tag or CSS class. and serve different purposes, and is not a valid Angular element.

In Angular, modules are inherently singletons. This means that once a module is loaded, it is cached and reused throughout the application. Even if it's lazily loaded in multiple places, the same instance is shared, reducing duplication and improving performance.

The most efficient way to structure routes in Angular for an admin dashboard with multiple sections and sub-sections is to use a hierarchical route structure with lazy-loaded modules. This approach promotes code-splitting and modularity, ensuring that each section and its related functionality are loaded only when needed.

When creating a custom async validator for a form control in frameworks like Angular, the validator should return an Observable to indicate a validation error. This allows you to handle asynchronous validation, such as making HTTP requests to validate the input. Observables provide a convenient way to handle async operations and emit error values when validation fails. Using other types like numbers, strings, or booleans would not be suitable for asynchronous validation scenarios.

The correct term to fill in the blank is "/secondary." When defining auxiliary routes in Angular, you typically prefix the route paths with "/secondary" to distinguish them from primary routes. This allows for multiple router outlets to display different views within the same page.

The ComponentFactoryResolver service in Angular is primarily used for dynamic component creation. It allows you to create components on the fly, which is useful for scenarios where you need to render components dynamically based on user interactions or other dynamic data. The other options are not the primary use cases for ComponentFactoryResolver.

In structural directives, you can access the container where you want to render the template by referencing it via the ng-container element. This element acts as a placeholder for rendering content conditionally or repeatedly, and it allows you to control where the template is inserted within the DOM based on your directive's logic.

The default change detection strategy in Angular is "Default" or "ChangeDetectionStrategy.Default." This strategy checks for changes in all components, regardless of whether their inputs have changed. It's the most conservative strategy and can have performance implications in large applications, as it checks for changes frequently. Developers often choose more optimized strategies like "OnPush" to improve performance.

Overusing dynamic components in an Angular application can lead to increased complexity of the application structure. While dynamic components offer flexibility, using them excessively can make the codebase harder to understand and maintain. It's essential to strike a balance between dynamic and static components to ensure a manageable and maintainable codebase. The other options do not represent common drawbacks of overusing dynamic components.

A core principle of the NgRx library is "Unidirectional Data Flow." It emphasizes that data flows in one direction through your application, making it easier to understand and reason about how data changes occur. This pattern helps manage state and side effects more predictably.