Nokea
Which of the following substances is most dense?
- A. A block of gold weighing 12g and having a volume of 4.6cm³
- B. A cube weighing 6g and having a volume of 0.91cm³
- C. A block weighing 143g and having a volume of 24.3cm³
- D. None of the above.
Correct Answer: B
Rationale: The correct answer is 'B: A cube weighing 6g and having a volume of 0.91cm³.' Density is calculated as mass divided by volume. For each option: A) 12g/4.6cm³ ≈ 2.61 g/cm³, B) 6g/0.91cm³ ≈ 6.59 g/cm³, C) 143g/24.3cm³ ≈ 5.88 g/cm³. Therefore, option B is the most dense with a density of approximately 6.59 g/cm³.
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What characterizes bases or alkaline solutions?
- A. Hydrogen acceptors
- B. Solutions of low pH
- C. Hydrogen donors
- D. Amphoteric
Correct Answer: A
Rationale: Bases or alkaline solutions are characterized by their ability to accept protons (hydrogen ions), making them hydrogen acceptors. When a base reacts with an acid, it accepts protons from the acid, forming water and a salt. This property distinguishes bases from acids, which donate protons. Therefore, the correct choice is A, as bases do not donate protons but instead accept them. This property allows bases to neutralize acids and regulate pH levels in solutions, making them crucial in maintaining the balance of acidity and alkalinity in various chemical systems.
Chemical reactions in living systems proceed along catabolic pathways, and there tends to be an increase in which of the following?
- A. Entropy
- B. Enthalpy
- C. Glucose
- D. Glycogen
Correct Answer: A
Rationale: In catabolic pathways, complex molecules are broken down into simpler ones, leading to an increase in disorder or entropy. Entropy represents the measure of randomness or disorder in a system. As chemical reactions break down molecules, the overall disorder in the system tends to increase, making entropy the correct answer in this context. Therefore, the correct answer is 'Entropy' as it aligns with the concept of increased disorder in catabolic pathways. Enthalpy, on the other hand, relates to the total heat content of a system and is not specifically associated with disorder or complexity. Glucose and glycogen are molecules involved in energy storage and are not directly related to the increase in disorder observed in catabolic pathways.
Which type of bond involves sharing pairs of electrons?
- A. Ionic
- B. Covalent
- C. Both
- D. None of the above
Correct Answer: B
Rationale: In a covalent bond, atoms share pairs of electrons to achieve a stable electron configuration. This sharing of electrons leads to the formation of a strong bond between atoms. Ionic bonds, on the other hand, involve the transfer of electrons from one atom to another. Therefore, the correct answer is option B, Covalent, as it specifically describes the sharing of electron pairs, distinguishing it from ionic bonds where electron transfer occurs rather than electron sharing.
What is the atomic number?
- A. Number of neutrons
- B. Number of protons
- C. Number of electrons
- D. Number of isotopes
Correct Answer: B
Rationale: The atomic number is the number of protons in an atom's nucleus. It uniquely identifies an element and determines its chemical properties. The number of neutrons and electrons can vary in an atom, but the number of protons remains constant for a specific element. Therefore, the correct answer is the 'Number of protons' (Choice B).
What role does carbonic acid play in the human body?
- A. Digests food
- B. Kills viruses
- C. Maintains pH of blood
- D. Grows hair
Correct Answer: C
Rationale: In the human body, carbonic acid, formed when carbon dioxide dissolves in water, plays a crucial role in maintaining the pH balance of blood. It acts as a buffer system, responsible for regulating blood acidity levels and preventing significant pH fluctuations that could harm the body. Choices A, B, and D are inaccurate as they do not reflect the actual function of carbonic acid in the human body.