2025 Midterm Reflection

A radioactive isotope has a half-life of 2.5 years. Which fraction of the original mass remains unchanged after 10. years?

• 1/2

• 1/4

• 1/8

• 1/16

Given the balanced equation: 2KI + F₂ → 2KF + I₂ Which type of chemical reaction does this equation represent?

• single replacement

• synthesis

• decomposition

• double replacement

Which element is listed with the number of protons in each of its atoms?

• silicon, 14

• nitrogen, 14

• oxygen, 16

• phosphorous, 16

A 1.0-gram sample of NaCl(s) is dissolved in 100. grams of water at 25°C, and another 1.0-gram sample of NaCl(s) is dissolved in 50. grams of water at 25°C. Which property of the two resulting mixtures will be different?

• polarity of the components in the mixture

• color of the components in the mixture

• particle size of the components in the mixture

• proportion by mass of the components in the mixture

Which radioisotope requires long-term storage to prevent the risk of biological exposure?

• Pu-239

• Au-198

• K-42

• N-16

A sample is composed of two different substances that can be separated by using filter paper. This sample is classified as

• an unsaturated solution

• a homogeneous mixture

• a heterogeneous mixture

• a single compound

A compound consists of two or more different elements that are

• chemically combined in a proportion that can vary

• physically mixed in a fixed proportion

• chemically combined in a fixed proportion

• physically mixed in a proportion that can vary

Which Lewis electron-dot diagram represents a molecule of H₂S?

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• 
• 
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Which atom forms an ion with a radius larger than the atomic radius?

• calcium atom

• lead atom

• oxygen atom

• tin atom

Which nuclear emission is listed with its notation?

• beta particle ⁰₋₁e

• proton ⁰₁β

• neutron ⁰₀γ

• alpha particle ¹₁P