The routerLink directive can be bound to an array, allowing you to pass parameters to the route. This is useful for passing dynamic data to routes, such as route IDs or other contextual information. While the routerLink can also be bound to other types of data, like arrays or queries, it's primarily used for passing parameters.

When two modules provide the same service and are imported into a third module in Angular, the service from the 'first' module will be used. Angular's dependency injection system follows a hierarchical order for providing services. The first module providing the service takes precedence over the second module, and so on. This ensures that the service is consistent and predictable in its usage.

In Angular's Reactive Forms, you can implement conditional form field validation by using a custom validator function. This function can check the value of one field and set the validation rules for another field accordingly. Template-driven forms are a different approach and do not provide as much flexibility in handling complex validation logic. Creating a new component for each form field is not the recommended approach for conditional validation, and Angular Material primarily deals with UI components, not the underlying validation logic.

The '*' syntax in directives like *ngIf and *ngFor is a syntactic sugar for using Template expressions. In Angular, Template expressions are embedded within double curly braces {{ }} and allow you to evaluate expressions, access properties, and perform other operations within the template. This syntax simplifies and enhances the readability of Angular templates.

To create a directive that listens for host events and reacts accordingly, you should use the @HostListener decorator. This decorator allows you to define event listeners directly within the directive class, making it easy to respond to events on the host element where the directive is applied.

To avoid unnecessary change detection cycles for components with data that doesn't change frequently, you can set their change detection strategy to ChangeDetectionStrategy.OnPush. This strategy makes the component's change detection dependent on its input properties, resulting in better performance. The Default strategy doesn't optimize for this scenario. Lazy and Smart are not valid change detection strategies in Angular.

In Angular, the *ngIf directive is used to conditionally display an element in the DOM. It evaluates an expression and only renders the associated element if the expression is true. This is commonly used for showing or hiding elements based on certain conditions. *ngFor is used for looping over arrays and rendering lists, not for conditional rendering. *ngSwitch is used for switching between multiple views based on a condition, and *ngClass is used for dynamically adding or removing CSS classes.

Immutable data structures, such as those provided by libraries like Immutable.js or using TypeScript's 'readonly' modifier, enhance performance in Angular applications by reducing the need for change detection. This is because changes to immutable data structures result in entirely new objects, making it easier for Angular to identify changes and update the view efficiently.

In Angular, the directive used to link to routes is routerLink. This directive is used in templates to generate hyperlinks that navigate to different views or components in an Angular application when clicked. The other options are not valid Angular directives for routing purposes.

In template-driven forms, the "ngMessage" directive (sometimes used as "ngMessages") is commonly used to display validation error messages. It is used in conjunction with "ngModel" to conditionally display error messages based on the validation state of the input field. The "ngMessage" directive allows you to define different error messages for various validation conditions.