Nursing Elites

1. Which of the following is a characteristic of a chemical change?

• A. Change in shape
• B. Production of gas
• C. Melting
• D. Freezing

Correct answer: B

Rationale: The production of gas is a characteristic of a chemical change. During a chemical change, new substances are formed, often with the release or absorption of energy. The production of gas is a significant indicator of a chemical change because it indicates the formation of new compounds through chemical reactions. Choices A, C, and D are not characteristics of chemical changes. Changes in shape, melting, and freezing are physical changes where the substance's identity remains the same, unlike in chemical changes where new substances with different properties are formed.

2. The three important allotropic forms of phosphorus are red, white, and ___________.

• A. green
• B. gray
• C. black
• D. silver

Correct answer: C

Rationale: The three important allotropic forms of phosphorus are red, white, and black. These forms indicate the different physical properties and reactivity of phosphorus under various conditions. Red phosphorus is more stable and less reactive than white phosphorus, while black phosphorus is the least reactive form. Choice C, 'black,' is the correct answer as it completes the sequence of allotropic forms of phosphorus. Choices A, 'green,' B, 'gray,' and D, 'silver,' are incorrect as they do not represent recognized forms of phosphorus.

3. How can the reaction rate of a chemical reaction be increased?

• A. Increase the temperature
• B. Increase the surface area
• C. Increase the concentration of reactants
• D. Add a catalyst

Correct answer: A

Rationale: To increase the reaction rate of a chemical reaction, one effective method is to increase the temperature. Raising the temperature provides more energy to the reacting particles, enabling them to collide more frequently and with higher energy, leading to an increase in the reaction rate. While increasing the surface area, concentration of reactants, and adding a catalyst are strategies that can also enhance the reaction rate, raising the temperature has the most direct and immediate impact. Increasing the surface area allows for more contact between reactants, increasing the concentration provides more reactant particles to collide, and adding a catalyst lowers the activation energy required for the reaction to occur. However, these methods may not have as immediate and significant an effect as increasing the temperature.

4. What is the oxidation state of the sulfur atom in sulfuric acid H2SO4?

• A. 4
• B. 6
• C. 8
• D. 10

Correct answer: B

Rationale: In sulfuric acid (H2SO4), sulfur has an oxidation state of +6. The oxidation state is determined by considering the overall charge of the compound and the known oxidation states of other elements. In this case, hydrogen is typically +1, and oxygen is -2. To balance the charges and match the compound's overall charge of 0, sulfur must have an oxidation state of +6. Choice A (4) is incorrect because it doesn't balance the charges in the compound. Choices C (8) and D (10) are also incorrect as they are not valid oxidation states for sulfur in this compound.

5. How can water be boiled at room temperature?

• A. By lowering the pressure
• B. By increasing the pressure
• C. By decreasing the volume
• D. By raising the boiling point

Correct answer: A

Rationale: The boiling point of water is directly affected by pressure. By lowering the pressure, water can boil at a lower temperature, even at room temperature. This occurs because at lower pressures, the molecules of water have less resistance to escaping into the vapor phase, thus enabling boiling to occur at lower temperatures. Choices B, C, and D are incorrect because increasing the pressure, decreasing the volume, or raising the boiling point would actually require higher temperatures to boil water rather than achieving boiling at room temperature.

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