Which of the following demonstrates correct APA number style?

The correct demonstration of APA number style is found in the choice that uses numerals for data or items that are part of a sequence, rather than writing them out in words. In APA style, numbers are typically represented as numerals when they are part of a label or a specific designation. For instance, in the phrase "Trial 3," the number "3" is shown as a numeral rather than being spelled out. This aligns with APA guidelines that instruct writers to use numerals for numbers in study designations, statistical results, and other specific types of numbered lists.

Other choices present written numbers where numerals would be more appropriate. For example, "Trial three" and "Chapter seven" both spell out the numbers rather than using numerals, which is less consistent with APA's stylistic preferences when dealing with labels or identifiers. "Table two" also spells out the number, making it less compliant with APA rules where numerals would be favored in such labeling conventions. Thus, "Trial 3" is the correct representation according to APA number style.