How many significant figures are there in the number 04560700?
- A. 4
- B. 5
- C. 7
- D. 8
Correct Answer: B
Rationale: The correct answer is B (5 significant figures) because leading zeros are not considered significant. In the number 04560700, the zeros before the 4 are placeholders and do not add to the precision of the number. Therefore, only the digits 4, 5, 6, 0, and 7 are significant. Choice A (4) is incorrect because it does not account for the zeros after the 6. Choice C (7) is incorrect as it counts all the digits including the leading zeros. Choice D (8) is incorrect as it includes all the digits, including non-significant zeros.
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Which of the following is an example of a quantitative observation?
- A. The piece of metal is longer than the piece of wood.
- B. Solution 1 is much darker than solution
- C. The liquid in beaker A is blue.
- D. The temperature of the liquid is 60°C.
Correct Answer: A
Rationale: The correct answer is A because it involves a measurable quantity (length) that can be expressed numerically. This is a quantitative observation as it can be described with numbers. Choices B and C describe qualities (color and appearance) which are qualitative observations. Choice D provides a quantitative measurement (temperature) but it is not an observation, rather a measurement.
Bromine exists naturally as a mixture of bromine-79 and bromine-81 isotopes. An atom of bromine-79 contains
- A. 35 protons, 44 neutrons, 35 electrons
- B. 34 protons and 35 electrons, only
- C. 44 protons, 44 electrons, and 35 neutrons
- D. 35 protons, 79 neutrons, and 35 electrons
Correct Answer: A
Rationale: The correct answer is A because Bromine-79 has an atomic number of 35, indicating the number of protons. Neutrons are calculated by subtracting the atomic number from the mass number, so Bromine-79 with a mass number of 79 has 44 neutrons. Electrons are equal to the number of protons in a neutral atom, so there are 35 electrons in an atom of Bromine-79.
Choice B is incorrect because it does not account for the correct number of neutrons present in Bromine-79. Choice C is incorrect as it has an incorrect number of protons and electrons for Bromine-79. Choice D is incorrect as it incorrectly assigns 79 neutrons to Bromine-79, which is the total mass number, not the number of neutrons.
Alpha particles beamed at thin metal foil may
- A. pass directly through without changing direction
- B. be slightly diverted by attraction to electrons
- C. be reflected by direct contact with nuclei
- D. A and C
Correct Answer: D
Rationale: The correct answer is D because when alpha particles are beamed at a thin metal foil, some pass directly through due to their small size and high energy (option A), while others are reflected by direct contact with nuclei in the metal foil (option C). This is based on the Rutherford scattering experiment which showed that alpha particles can be deflected by the positive nuclei in the metal foil. Option B is incorrect as alpha particles are not diverted by attraction to electrons in the foil. Option D combines the correct explanations for the behavior of alpha particles when beamed at thin metal foil.
The chemist credited for inventing a set of symbols for writing elements and a system for writing the formulas of compounds (and for discovering selenium, silicon, and thorium) is
- A. Boyle
- B. Lavoisier
- C. Priestly
- D. Berzelius
Correct Answer: D
Rationale: The correct answer is D: Berzelius. Berzelius is credited with inventing symbols for elements and a system for writing compound formulas. He also discovered selenium, silicon, and thorium. Berzelius made significant contributions to the field of chemistry.
A: Boyle is known for Boyle's Law related to gases, not for inventing chemical symbols or discovering elements.
B: Lavoisier is known as the father of modern chemistry but did not invent chemical symbols or discover these elements.
C: Priestly is known for discovering oxygen, but not for the specific contributions mentioned in the question.
All of the following are true except:
- A. Ions are formed by adding electrons to a neutral atom.
- B. Ions are formed by changing the number of protons in an atom's nucleus.
- C. Ions are formed by removing electrons from a neutral atom.
- D. An ion has a positive or negative charge.
Correct Answer: B
Rationale: The correct answer is B because changing the number of protons in an atom's nucleus would result in a different element, not an ion.
A: True - adding or removing electrons forms ions.
C: True - removing electrons forms positively charged ions.
D: True - ions have a charge due to the imbalance of protons and electrons.