ACT^® Science Practice Test

Free ACT Science Practice Test (updated 2026)

The Science section of the ACT^® evaluates your knowledge of various science concepts, including data analysis, graphs, experiments, and formulating predictions.

 
To help you prepare for this section of the ACT, this page contains everything you need to know, including what topics are covered, how many questions there are, and how you can study effectively.

Click “Start Test” above to take a free ACT Science practice test!

What’s on the ACT Science Section?

ACT Science Practice Questions

One of the best ways to test your knowledge is by taking a practice test. Evaluate your science knowledge by trying your hand at the three practice questions below!

Answer each question and read through the answer explanation, whether you got the answer right or wrong. This will help you ensure you’ve got the topic mastered.

Whether you struggled with these questions or aced them on your first try, be sure to take the full practice test to get a better idea of how prepared you really are!

1. Read the passage below before answering the question:

Read Passage

A scientist wishes to test the effectiveness of an antibiotic. To do this, she takes nine Petri dishes filled with agar, a nutrient substrate on which bacteria grow readily, and labels them with the numbers 1 through 9. She then introduces bacterial cultures into each Petri dish, taking care to spread them evenly along the surfaces.

In dishes 1 through 3, the scientist then places a drop of solution of the antibiotic to be tested at a concentration of 2 parts per thousand. (The rest of the solution is water.) She does the same to dishes 4 through 6 but with a solution at a concentration of one part per thousand. In dishes 7 through 9, the scientist places a drop of a control liquid. The scientist covers the Petri dishes, leaves them in a cool location for five days, and then examines the results. The diagrams below show the growth of bacteria in each dish after five days; the gray areas show where on the Petri dish bacterial cultures have grown, whereas the white areas show parts of the agar that are clear of bacteria.

What is the best conclusion that can be drawn from the given data?

A. The antibiotic has no effect on bacterial growth. B.  The antibiotic has an effect on bacterial growth that increases with its concentration. C.  The antibiotic impedes bacterial growth, but increasing the concentration above one part per thousand does not increase the effect. D.  The antibiotic is only effective at concentrations greater than one part per thousand. Submit

All the Petri dishes treated with the antibiotic show a clear circle free of bacterial growth. It is clear that the antibiotic impedes bacterial growth at both tested concentrations. However, there is no obvious significant difference between the dishes treated with the antibiotic solution at a concentration of one part per thousand and those treated with a solution at a concentration of two parts per thousand. This means that the effect does not necessarily scale with increasing concentration.

Found a bug? Let us know!

2. Read the passage below before answering the question:

Read Passage

A phase diagram is a chart that shows what physical state a substance is in—solid, liquid, or gas—at different temperatures and pressures. Typically, the axes of a phase diagram are labeled with temperature on the \(x\)-axis and pressure on the \(y\)-axis.

Below is shown the phase diagram for molecular nitrogen:

Consider the points labeled A, B, and C on the diagram. How would the volume of a quantity of gas at the temperature and pressure indicated at points B and C compare to the volume of the same quantity of gas at the temperature and pressure indicated at point A?

A. \(V_B\gt V_A, V_C\gt V_A\) B.  \(V_B\lt V_A, V_C\lt V_A\) C.  \(V_B\gt V_A, V_C\lt V_A\) D.  \(V_B\lt V_A, V_C\gt V_A\) Submit

From the ideal gas law, \(PV=nRT\), we expect that for a particular quantity of gas, the volume is directly proportional to the temperature and inversely proportional to the pressure. The pressure at point B is higher than at point A which, because volume is inversely proportional to pressure, means the volume is lower. The temperature at point C is higher than at point A which, because volume is directly proportional to temperature, means the volume is higher.

Found a bug? Let us know!

3. Read the passage below before answering the question:

Read Passage

Researchers investigated how water temperature affects the amount of time required for a tablet to dissolve. They filled four identical beakers with 200 mL of water at different temperatures. They placed one identical tablet into each beaker and recorded the time required for the tablet to dissolve completely.

Water Temperature (°C)	Required Time for Tablet to Dissolve (Seconds)
10	184
20	132
30	91
40	63

Based on the results, if the researchers repeated the experiment using water at 35°C, the tablet would most likely dissolve in:

A. less than 63 seconds B.  between 63 and 91 seconds C.  between 91 and 132 seconds D.  more than 184 seconds Submit

As the water temperature increased, the time required for the tablet to dissolve decreased. At 30°C, the tablet dissolved in 91 seconds, and at 40°C, it dissolved in 63 seconds. Therefore, at 35°C, the tablet would most likely dissolve in a time between 63 and 91 seconds.

Found a bug? Let us know!

ACT Online Prep Course

If you want to be fully prepared, Mometrix offers an online ACT prep course designed to give you everything you need to succeed!

Here’s what you’ll find in the ACT course:

Everyone learns differently, so we’ve tailored the ACT online prep course to ensure every learner has what they need to prepare for the ACT exam.

Click below to check it out!

FAQs

By Peter Rench

Peter Rench joined Mometrix in 2009 and serves as Vice President of Product Development, responsible for overseeing all new product development and quality improvements. Mr. Rench, a National Merit Scholar, graduated magna cum laude with a Bachelor of Science in Mechanical Engineering and a minor in mathematics from Texas A&M University.

Edited by Aaron Lanni

Aaron is the content manager and lead editor for Mometrix Academy. He regularly produces, updates, proofreads, and edits content to ensure it meets Mometrix’s quality and accessibility standards.

Learn more about our editorial guidelines →

ACT® is a registered trademark belonging to ACT Education Corp. (“ACT”). ACT is not involved with or affiliated with Mometrix Media LLC, nor does ACT endorse or sponsor any of the products or services offered by Mometrix Media LLC.