HESI A2 Chemistry Practice Test

Correct Answer: A

Rationale: The correct answer is A: Covalent bonds. Covalent bonds involve a complete sharing of electrons between atoms with partially filled outer shells. This sharing allows atoms to achieve stable electron configurations. Hydrogen bonds involve an electrostatic attraction between a hydrogen atom and a highly electronegative atom. Proportional bonds are not a recognized type of chemical bond. Choice D, N/A, is not a valid option for this question.

Correct Answer: B

Rationale: The correct answer is B: Alpha radiation. Alpha radiation emits helium ions, which are essentially helium nuclei. These particles are large and have a low penetrating ability, so they can be stopped by a piece of paper. Beta radiation (choice A) consists of fast-moving electrons and can penetrate paper but can be stopped by aluminum. Gamma radiation (choice C) is high-energy electromagnetic radiation that requires thick lead or concrete to stop. X-ray radiation (choice D) is similar to gamma radiation and also requires dense materials for shielding. Therefore, alpha radiation is the only type that fits the description of emitting helium ions and being stopped by a piece of paper.

Correct Answer: C

Rationale: The correct answer is C: Representative elements. S block and p block elements collectively make up the representative elements in the periodic table. S block elements are the alkali metals and alkaline earth metals, while p block elements include nonmetals, metalloids, and halogens. These elements are called representative elements because they represent the diverse chemical properties found in the periodic table. Transition elements (A) are the d block elements, not the s and p block elements. Active elements (B) and inactive elements (D) are not specific terms used to categorize elements in the periodic table.

Correct Answer: B

Rationale: The correct answer is B: -2. In most compounds, oxygen has an oxidation number of -2 due to its high electronegativity. Oxygen typically gains electrons in chemical reactions. This is consistent with the octet rule, where oxygen achieves a stable electron configuration by gaining two electrons. Choices A, C, and D are incorrect as oxygen rarely has an oxidation number of 2, 0, or -1 in compounds. Oxygen's oxidation number is -2 in the majority of cases, making choice B the correct answer.

Correct Answer: D

Rationale: Rationale: 1. Wavelength is defined as the distance between adjacent peaks or troughs on a wave. 2. Frequency is the number of wave cycles per unit time, not the distance between peaks/troughs. 3. Wavenumber is the spatial frequency of a wave, not the distance between peaks/troughs. 4. Wave oscillation refers to the movement of particles in a wave, not the distance between peaks/troughs. Summary: The correct answer is D because wavelength specifically refers to the distance between adjacent peaks or troughs on a wave, whereas the other choices are related to different properties of waves.