Nokea
What is the charge on potassium in the compound KCl?
- A. -1
- B. +1
- C. -2
- D. +2
Correct Answer: B
Rationale: In the compound KCl, the overall charge must be zero since it is a neutral compound. Chlorine (Cl) typically has a charge of -1 in ionic compounds. Therefore, for the compound to be neutral, potassium (K) must have a charge of +1 to balance the -1 charge of chlorine. This results in a total charge of 0 for the compound. Thus, the correct answer is +1. The positively charged potassium ion (K+) combines with the negatively charged chloride ion (Cl-) to form an electrically neutral compound, potassium chloride (KCl).
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An element has 6 protons, 6 electrons, and 6 neutrons. What is its atomic number?
- A. 6
- B. 12
- C. 18
- D. Not enough information
Correct Answer: A
Rationale: The atomic number of an element is determined by the number of protons in its nucleus. Since the element in question has 6 protons, its atomic number is also 6. The number of neutrons and electrons does not impact the atomic number, which is solely based on the number of protons. Therefore, the correct answer is A: 6.
A carbon atom with fewer neutrons than a neutral carbon atom is known as what?
- A. Isotope
- B. Ion
- C. Both are correct
- D. None of the above
Correct Answer: A
Rationale: The correct answer is 'Isotope.' An isotope is a variant of a chemical element that has the same number of protons but a different number of neutrons in its nucleus. In this scenario, a carbon atom with fewer neutrons than a neutral carbon atom represents a different isotope of carbon with a distinct atomic mass. The difference in neutron count does not alter the atom's charge, ruling out the possibility of it being an ion. Therefore, the appropriate term to describe this situation is 'Isotope.'
Which of the following statements is most accurate regarding the compound 2Hâ‚‚O?
- A. 2Hâ‚‚O has a total of 2 hydrogen atoms.
- B. 2Hâ‚‚O represents two water molecules.
- C. Hâ‚‚O represents two water molecules.
- D. None of the above.
Correct Answer: B
Rationale: The chemical formula 2Hâ‚‚O represents two water molecules. Each water molecule (Hâ‚‚O) consists of 2 hydrogen atoms and 1 oxygen atom. Therefore, 2Hâ‚‚O denotes two separate water molecules, making choice B the correct statement
Which of the following is not an organic compound?
- A. Hâ‚‚O
- B. C₂H₆
- C. C₃H₇O₂
- D. None of the above
Correct Answer: A
Rationale: The correct answer is 'A: H₂O.' An organic compound is defined as a compound that contains carbon and hydrogen atoms bonded together. Choice A, H₂O (water), is composed of hydrogen and oxygen but lacks carbon, making it an inorganic compound. Choices B (C₂H₆) and C (C₃H₇O₂) both contain carbon and hydrogen, thus meeting the criteria for organic compounds. Therefore, the correct answer is A, H₂O, as it does not meet the definition of an organic compound due to the absence of carbon in its structure.
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.