Nursing Elites

1. Cobalt-60 has a half-life of 5 years. If you start with 20 g of cobalt-60, how much is left after 10 years?

• A. 15 g
• B. 10 g
• C. 5 g
• D. 2.5 g

Correct answer: C

Rationale: Cobalt-60's half-life of 5 years means that after 5 years, half of the initial amount remains. Therefore, after 10 years, a quarter (half of a half) of the initial amount will remain. Starting with 20 g, after 10 years, 5 g of cobalt-60 will be left. Choice A (15 g) is incorrect because it assumes a linear decrease, not considering the exponential decay characteristic of radioactive substances. Choice B (10 g) is incorrect as it overlooks that after 10 years, more decay has occurred. Choice D (2.5 g) is incorrect as it represents only an eighth of the initial amount after 10 years, not a quarter.

2. Which elements are typically involved in hydrogen bonding?

• A. Carbon, hydrogen, oxygen
• B. Fluorine, chlorine, oxygen
• C. Fluorine, chlorine, nitrogen
• D. Fluorine, oxygen, nitrogen

Correct answer: D

Rationale: Hydrogen bonding occurs between hydrogen and highly electronegative atoms such as fluorine, oxygen, and nitrogen. These atoms have a strong pull on the shared electrons, leading to a partial negative charge on them, which allows them to form hydrogen bonds with hydrogen or other electronegative atoms. Choice A is incorrect because carbon is not typically involved in hydrogen bonding. Choice B is incorrect because chlorine is not as electronegative as nitrogen, and choice C is incorrect because nitrogen is more electronegative than chlorine.

3. What is the name of the force that holds ionic compounds together?

• A. Covalent bonds
• B. Ionic bonds
• C. Hydrogen bonds
• D. Metallic bonds

Correct answer: B

Rationale: Ionic bonds are the forces that hold ionic compounds together. In ionic compounds, positively and negatively charged ions are held together by electrostatic forces of attraction, forming a stable structure. Covalent bonds involve the sharing of electrons between atoms, not the transfer of electrons like in ionic bonds. Hydrogen bonds are a type of intermolecular force, not the primary force in holding ionic compounds together. Metallic bonds are found in metals and involve a 'sea of electrons' that hold metal atoms together, different from the electrostatic attraction between ions in ionic compounds.

4. What is the correct formula for calcium carbonate?

• A. CaSO₃
• B. CaCO₃
• C. Ca(OH)₂
• D. CH₃OH

Correct answer: B

Rationale: The correct formula for calcium carbonate is CaCO₃, which consists of one calcium (Ca) atom, one carbon (C) atom, and three oxygen (O) atoms. Therefore, choice B, CaCO₃, is the accurate formula for calcium carbonate. Choices A, C, and D do not represent the correct formula for calcium carbonate. Choice A, CaSO₃, is calcium sulfite, not calcium carbonate. Choice C, Ca(OH)₂, is calcium hydroxide, and choice D, CH₃OH, is methanol, none of which are correct formulas for calcium carbonate.

5. Arsenic and silicon are examples of ___________.

• A. metals
• B. nonmetals
• C. metalloids
• D. heavy metals

Correct answer: C

Rationale: Arsenic and silicon are both examples of metalloids. Metalloids have properties that lie between those of metals and nonmetals. They exhibit characteristics of both groups, making them versatile elements with various applications in different industries. Choice A (metals) is incorrect as arsenic and silicon do not exhibit typical metallic properties. Choice B (nonmetals) is incorrect as they do not possess all the properties of nonmetals. Choice D (heavy metals) is incorrect as heavy metals refer to a different group of elements with high atomic weights, and arsenic and silicon are not categorized as heavy metals.

Similar Questions