Step 1: Understand the question.
We must choose the correct full form of the file extension pptx.
Step 2: Where pptx comes from.
The pptx format is the default save type for Microsoft PowerPoint, used since Office 2007.
Step 3: The XML clue.
The letter x at the end stands for XML. After Office 2007, Microsoft moved its files to the Open XML standard for better compression and structure.
Step 4: Build the full form.
Putting it together, pptx means PowerPoint Open XML Presentation. The ppt part is PowerPoint and the file holds a presentation.
Step 5: Reject the wrong options.
Names like Power Point Extension, Expansion, or Extra Version are not official terms. They just guess from the letters.
Step 6: Conclude.
So the answer is option 2, Power Point Open XML Presentation.
\[ \boxed{\text{Power Point Open XML Presentation}} \]