Which one of the following statements about atomic structure is false?

Correct Answer: D

Rationale: The correct answer is D because the statement that the number of protons and neutrons is always the same in a neutral atom is false. In a neutral atom, the number of protons equals the number of electrons, not the number of neutrons. Neutrons are not always equal to the number of protons. A: An atom is mostly empty space - Correct. This is true because the nucleus is very tiny compared to the overall size of the atom. B: Almost all of the mass of the atom is concentrated in the nucleus - Correct. This is true because protons and neutrons have much more mass than electrons. C: The protons and neutrons in the nucleus are very tightly packed - Correct. This is true because protons and neutrons are densely packed within the nucleus.

Correct Answer: A

Rationale: The correct answer A is determined by knowing that the atomic number of rhenium is 75. Since the element is rhenium-185, the sum of protons and neutrons must equal 185. As the atomic number is 75, the number of protons is 75. Therefore, the number of neutrons is 185 - 75 = 110. Thus, rhenium-185 has 75 protons and 110 neutrons. Choices B, C, and D are incorrect as they do not adhere to the correct number of protons and neutrons in the nucleus of rhenium-185.

Correct Answer: A

Rationale: The correct answer is A. Since the question states that there are 20 protons, option A with 22 protons is incorrect. Option B with 20 protons matches the given information, making it the correct answer. Option C with 18 electrons is unrelated to the given information about protons. Option D with just the number 22 is irrelevant and does not provide any information about protons.

Correct Answer: C

Rationale: The correct answer is C: 19 p, 20 n, 19 e. K+ has an atomic number of 19, indicating 19 protons. Since it is a potassium ion with a +1 charge, it lost one electron, giving it 19 electrons instead of the usual 20. The number of neutrons is found by subtracting the atomic number from the mass number (39 for potassium) to get 20 neutrons. Option A is incorrect due to the incorrect number of electrons. Option B has the incorrect number of protons. Option D has the incorrect number of electrons.

Correct Answer: B

Rationale: The formula for water is H₂O, indicating there are two hydrogen atoms and one oxygen atom per molecule. This is because the subscript 2 in H₂ represents two hydrogen atoms, and O represents one oxygen atom. Therefore, choice B is correct. Choices A, C, and D are incorrect because they do not accurately represent the composition of water molecules. Choice A suggests twice as much mass of hydrogen than oxygen, which is not true. Choice C suggests twice as much mass of oxygen than hydrogen, which is also incorrect. Choice D implies there are two oxygen atoms in a water molecule, which is inaccurate.