The correct answer is D. Component visibility filter.
In Lightning App Builder, component visibility rules can control whether a component appears based on context, including the device/form factor. Salesforce Trailhead specifically describes creating a visibility rule so a component appears only when the page is viewed on a phone, which matches restricting a Lightning component to mobile users.
A is incorrect because form factor settings are generally used for page/device availability or preview behavior, not the best feature for hiding or showing one specific component on a single Lightning record page.
B and C are incorrect because the Highlights Panel and Related List Quick Links are page components, not conditional visibility tools.

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The correct answer is B. Use field-level security on page layouts with record types to restrict editing fields.
The requirement changes after the Opportunity is closed. The best configuration is to use record types with assigned page layouts so the closed Opportunity layout can make most fields read-only while allowing the Sales Operations team to edit the two post-close fields. Salesforce page layouts can control which fields are visible, read-only, or required, and page layouts can be assigned by profile and record type.
A is incomplete because it does not account for different behavior after close. C is incorrect because field sets are not used for page-layout field editability. D is too broad because it would make fields read-only for the Sales profile regardless of Opportunity stage.

The correct answer is D. Create an Apex Trigger on the Account object.
The requirement is conditional: allow Account deletion generally, but block deletion when the Account has open Opportunities. A validation rule is not the correct tool because validation rules evaluate record data during save operations, while this requirement is specifically about preventing a delete operation.
An Apex before delete trigger can query related open Opportunities and call addError() on the Account record to stop the delete. Salesforce Apex documentation confirms that triggers can run before or after delete events, and trigger errors can prevent DML operations from completing.
A is incorrect because removing Delete permission blocks all Account deletion.
B is incorrect because removing the Delete button is not security and does not stop deletion through other channels.
C is incorrect because validation rules are not the right mechanism to block conditional deletes.

The correct answers are A. Create a child record, C. Update a related record, and D. Send an email alert.
Process Builder was designed to automate repetitive business actions. Salesforce documentation describes Process Builder as a tool for automating tasks, emails, and record updates.
Process Builder can improve productivity by performing actions such as:
Create a child record - Process Builder can create a record when criteria are met.
Update a related record - Process Builder can update the record that started the process or related records.
Send an email alert - Salesforce documentation specifically states that a process can send an email by using an email alert.
B is incorrect because "Start an additional message" is not a standard Process Builder productivity capability.
E is incorrect because Process Builder does not delete related records as a standard declarative action.

The correct answers are B. External ID and C. Unique.
The legacy ID field should be marked as External ID because Salesforce can use an external ID field to match records during import, integration, and upsert operations. Salesforce documentation confirms that external IDs can be used to create or update records through upsert.
The field should also be marked Unique so Salesforce prevents duplicate legacy ID values. Salesforce custom field attribute documentation states that the Unique option prevents duplicate field values.
Why others are incorrect:
A is incorrect because encrypted text is not the right choice for a matching legacy ID used in upserts.
D is not the best answer because making the field required does not enable upsert matching or prevent duplicate external IDs.