- A
The screen protector is incompatible with the phone model.
Why wrong: While incompatibility can cause fit issues, bubbles and lifting edges are more commonly due to installation errors rather than the protector being the wrong size.
- B
The phone's screen has a manufacturing defect.
Why wrong: A screen defect could cause display issues, but it would not cause a screen protector to bubble or lift after installation.
- C
The user did not properly clean the screen before installation.
Dust, oil, or moisture left on the screen prevents the adhesive from bonding evenly, leading to bubbles and lifting edges. This is the most common cause of such issues.
- D
The screen protector is a tempered glass type, which is prone to bubbles.
Why wrong: Tempered glass protectors are actually less prone to bubbles than plastic ones when installed correctly. The issue is not inherent to the material.
Quick Answer
The answer is improper installation, specifically failing to clean the screen thoroughly before applying the protector. This is the most likely cause because even microscopic dust, oil, or residue creates gaps between the glass and the adhesive layer, preventing a perfect seal. As the adhesive cures over the first 48 hours, trapped particles cause central bubbles, while edge lifting occurs when the adhesive cannot bond to a contaminated surface. On the CompTIA A+ Core 1 220-1201 exam, this question tests your understanding of mobile device maintenance and common user errors—a frequent trap is blaming the protector’s quality rather than the installation process. Remember the memory tip: “Clean before you seal” to avoid bubbles that reveal.
220-1201 Mobile Device Accessories Practice Question
This 220-1201 practice question tests your understanding of mobile device accessories. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A user reports that their smartphone's screen protector has a large bubble in the center and the edges are lifting. They installed it themselves two days ago. What is the most likely cause of this issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The user did not properly clean the screen before installation.
Screen protector bubbles and lifting edges are almost always caused by improper installation, such as not cleaning the screen thoroughly or not aligning the protector correctly. Even high-quality protectors will fail if the surface isn't perfectly clean and dust-free. The correct answer is improper installation.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The screen protector is incompatible with the phone model.
Why it's wrong here
While incompatibility can cause fit issues, bubbles and lifting edges are more commonly due to installation errors rather than the protector being the wrong size.
- ✗
The phone's screen has a manufacturing defect.
Why it's wrong here
A screen defect could cause display issues, but it would not cause a screen protector to bubble or lift after installation.
- ✓
The user did not properly clean the screen before installation.
Why this is correct
Dust, oil, or moisture left on the screen prevents the adhesive from bonding evenly, leading to bubbles and lifting edges. This is the most common cause of such issues.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
The screen protector is a tempered glass type, which is prone to bubbles.
Why it's wrong here
Tempered glass protectors are actually less prone to bubbles than plastic ones when installed correctly. The issue is not inherent to the material.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 220-1201 NAT questions on configuration and troubleshooting.
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Mobile Device Accessories — study guide chapter
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Mobile Device Accessories practice questions
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FAQ
Questions learners often ask
What does this 220-1201 question test?
Mobile Device Accessories — This question tests Mobile Device Accessories — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The user did not properly clean the screen before installation. — Screen protector bubbles and lifting edges are almost always caused by improper installation, such as not cleaning the screen thoroughly or not aligning the protector correctly. Even high-quality protectors will fail if the surface isn't perfectly clean and dust-free. The correct answer is improper installation.
What should I do if I get this 220-1201 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 220-1201 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 18, 2026
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