A UX Design team is doing a review of a new Lightning Web Component (LWC).

The correct answer is C. `slds--size-1-of-2`, which the uploaded study guide explicitly identifies as the class that does not follow the expected SLDS convention. SLDS uses a structured naming system derived from Block-Element-Modifier (BEM) conventions. Salesforce documentation describes a block as the primary component, an element as a constituent part represented with a double underscore, and a modifier as a variation or state.

Current Salesforce guidance is particularly relevant here. Modern SLDS notation uses the single underscore for modifier syntax. For example, `slds-avatar_circle` correctly represents the circular avatar variant. `slds-box` is itself a valid SLDS utility/component class. Salesforce also confirms that older double-dash modifier syntax has been deprecated in favor of the single-underscore convention. Option C is malformed because the separator appears immediately after the `slds` namespace: `slds--size-1-of-2`. Even historical sizing syntax would have been structured around the size class, such as `slds-size--1-of-2`, rather than `slds--size-1-of-2`. Modern notation uses forms such as `slds-size_1-of-2`. Therefore, C clearly violates the expected SLDS class structure.

Study Guide reference/topics: SLDS, BEM naming, CSS classes, modifiers, Lightning Web Components.

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