Nursing Elites

1. A radioactive isotope has a half-life of 20 years. How many grams of a 6-gram sample will remain after 40 years?

• A. 8
• B. 6
• C. 3
• D. 1.5

Correct answer: C

Rationale: The half-life of a radioactive isotope is the time it takes for half of the original sample to decay. After each half-life period, half of the initial sample remains. In this case, after the first 20 years, half of the 6-gram sample (3 grams) will remain. After another 20 years (total of 40 years), half of the remaining 3 grams will remain, which is 1.5 grams. Therefore, 3 grams will be left after 40 years. Choice A is incorrect as it doesn't consider the concept of half-life and incorrectly suggests an increase in the sample. Choice B is incorrect as it assumes no decay over time. Choice D is incorrect as it miscalculates the remaining amount after two half-life periods.

2. What is the coefficient of O after the following equation is balanced?

• A. 1
• B. 2
• C. 3
• D. 4

Correct answer: A

Rationale: In a balanced chemical equation, the coefficient of oxygen (O) in O2 is already 2, so there is no need to adjust its coefficient further. Therefore, the coefficient of O remains as 1. Since the coefficient of O2 is 2, each O atom is represented by the coefficient of 1, and it does not change during the balancing process. Choices B, C, and D are incorrect as they suggest changing the coefficient of oxygen, which is not necessary for O2 in a balanced equation.

3. If electrons are shared equally in a covalent bond, the bond is classified as what?

• A. Polar
• B. Non-polar
• C. Ionic
• D. Hydrogen

Correct answer: B

Rationale: The correct answer is B: Non-polar. In a non-polar covalent bond, electrons are shared equally between the atoms involved, leading to a balanced distribution of charge and no significant difference in electronegativity between the atoms. This equal sharing results in a non-polar bond. Choices A, C, and D are incorrect because a polar bond involves an unequal sharing of electrons, an ionic bond is formed by the transfer of electrons, and a hydrogen bond is a specific type of non-covalent bond.

4. Which of the following represents a hydride ion?

• A. H⁻
• B. H⁺
• C. OH⁻
• D. HCl

Correct answer: A

Rationale: The hydride ion is denoted by H⁻, indicating that it has gained an extra electron to complete its valence shell, resulting in a full octet and a net charge of -1. This ion is commonly found in metal hydrides and plays a significant role in various chemical reactions. Option B, H⁺, represents a proton with a positive charge. Option C, OH⁻, represents the hydroxide ion, consisting of oxygen and hydrogen. Option D, HCl, is a compound composed of hydrogen and chlorine ions, not a hydride ion.

5. What is the correct electron configuration for carbon?

• A. 1s²2s²2p¹
• B. 1s²2s²2p²
• C. 1s²2s²2p³
• D. 1s²2s²2p⁶3s¹

Correct answer: B

Rationale: The correct electron configuration for carbon is 1s²2s²2p². This configuration indicates that there are 2 electrons in the first energy level (1s²), 2 electrons in the second energy level (2s²), and 2 electrons in the second energy level (2p²). It adheres to the aufbau principle, which states that electrons fill orbitals starting from the lowest energy level, and the Pauli exclusion principle, which states that each electron in an atom must have a unique set of quantum numbers. Choice A is incorrect because it does not fill the 2p orbital correctly. Choice C is incorrect as it exceeds the number of possible electrons in the 2p orbital. Choice D is incorrect as it includes an electron in the 3s orbital, which is not part of the electron configuration for carbon.

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