Free ACT Evaluating Models and Conclusions practice questionsEnhanced ACT, 2026 format
Do the data support a hypothesis? Which scientist's view does a new finding favor? These questions test reasoning from evidence, not science knowledge.
Answer each question, then read why the right answer is right and why the tempting one is wrong.
Question 1
Science
The Moon's composition is similar to that of Earth's mantle, but the Moon has a much smaller iron core, relative to its size, than Earth does. Two scientists discuss how the Moon formed.
Scientist 1
The Moon formed when a Mars-sized body struck the early Earth about 4.5 billion years ago (the giant-impact hypothesis). The collision ejected material from Earth's outer layers, which had already separated from the iron-rich core. This debris orbited Earth and coalesced into the Moon. Because the debris came mostly from the mantle of Earth and the impactor, the Moon is poor in iron. Computer simulations of such impacts produce a Moon of the correct mass. The ratios of oxygen isotopes in lunar rocks are nearly identical to those in Earth rocks, which is expected if most lunar material came from Earth.
Scientist 2
The Moon formed by co-accretion: Earth and the Moon condensed together from the same region of the solar nebula, growing side by side. This explains why lunar and terrestrial oxygen isotopes match — both bodies formed from the same material. The Moon has a small iron core because most metallic iron in the region was swept up by the larger, faster-growing Earth. A giant impact would have heated the debris so strongly that volatile elements such as potassium and sodium would have been lost, yet lunar rocks contain measurable amounts of these elements.
Both scientists agree that the Moon is about 4.5 billion years old and that its oxygen isotope ratios closely match Earth's.
According to Scientist 1, the Moon has a small iron core because:
Question 2
Science
Soil respiration is the release of carbon dioxide (CO₂) from soil by plant roots and microorganisms. Ecologists measured soil respiration rate (in grams of carbon per square meter per day, g C/m²/day) monthly for one year at three sites in a temperate forest. Site A is a mature stand of oak; Site B was clear-cut 2 years before the study; Site C was clear-cut 15 years before the study and has regrown as young maple. Table 1 gives selected monthly values.
Table 1
Month | Soil temp (°C) | Site A | Site B | Site C
January | 1 | 0.4 | 0.3 | 0.4
April | 8 | 1.6 | 0.9 | 1.5
July | 19 | 4.8 | 2.1 | 4.1
October | 11 | 2.2 | 1.2 | 2.0
The ecologists noted that root respiration accounts for roughly half of total soil respiration in intact forest.
Based on Figure 2 and the description of the sites, which of the following best explains why Site C's annual respiration was much closer to Site A's than Site B's was?
Question 3
Science
The apparent brightness of a light source decreases with distance. Astronomers describe brightness on a magnitude scale in which a LARGER number means a DIMMER object; a difference of 5 magnitudes corresponds to a factor of 100 in brightness. A star's absolute magnitude is the apparent magnitude it would have at a standard distance of 10 parsecs (pc). Table 1 lists six stars.
Table 1
Star | Apparent magnitude | Absolute magnitude | Distance (pc) | Surface temperature (K)
A | 0.0 | −3.0 | 40 | 9,500
B | 2.1 | 2.1 | 10 | 5,800
C | 4.8 | −0.2 | 100 | 3,400
D | 6.5 | 11.5 | 1.0 | 3,100
E | 1.3 | −4.7 | 160 | 22,000
F | 3.7 | 3.7 | 10 | 6,100
Figure 1 plots absolute magnitude against surface temperature for the six stars, with a dashed line marking the band along which most stars fall. Following astronomical convention, hotter stars are plotted to the LEFT and brighter (smaller) magnitudes toward the TOP.
Note: For a given surface temperature, a star that is brighter in absolute magnitude than the band predicts must be larger in radius.
Based on Figure 1 and the note, which stars are most likely much larger in radius than the other stars of similar temperature?
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