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How many oxygen atoms are in 2Oâ‚‚?
- A. 2
- B. 4
- C. 1
Correct Answer: B
Rationale: The chemical formula 2OÄ‚‚ represents two molecules of oxygen, where each molecule contains two oxygen atoms. To find the total number of oxygen atoms, you multiply the number of molecules (2) by the number of atoms in each molecule (2), which equals 4 oxygen atoms in total.
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Which subatomic particle does not contribute significantly to an atom's mass?
- A. Proton
- B. Neutron
- C. Electron
- D. All contribute to the atom's mass.
Correct Answer: C
Rationale: Electrons do not contribute significantly to an atom's mass. Protons and neutrons are much more massive than electrons and make up the majority of an atom's mass. Electrons have a very small mass compared to protons and neutrons, and their contribution to the total mass of an atom is considered negligible. Therefore, the correct answer is C, Electrons.
What is 119 K in degrees Celsius?
- A. 32C
- B. -154C
- C. 154C
- D. -32C
Correct Answer: B
Rationale: To convert from Kelvin to Celsius, you subtract 273.15 from the temperature in Kelvin. Therefore, 119 K - 273.15 = -154C. Hence, 119 K is equivalent to -154C. The correct answer is -154C, as it results from the conversion formula from Kelvin to Celsius.
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.
Which type of bond involves atoms gaining or losing electrons?
- A. Ionic
- B. Covalent
- C. Both
- D. Neither
Correct Answer: A
Rationale: Ionic bonds involve the transfer of electrons between atoms, leading to one atom gaining electrons (becoming negatively charged) while the other loses electrons (becoming positively charged). This results in the formation of ions that are held together by electrostatic forces, creating an ionic bond. In a covalent bond, atoms share electrons rather than gaining or losing them, making option A, 'Ionic,' the correct answer to this question. Therefore, the correct answer is 'Ionic,' as it specifically involves gaining or losing electrons to form a bond.
What does the term 'atomic number' represent?
- A. Number of neutrons
- B. Number of protons
- C. Number of electrons
- D. Number of isotopes
Correct Answer: B
Rationale: The atomic number represents the number of protons in the nucleus of an atom. This number uniquely identifies an element and determines its placement in the periodic table. The number of neutrons and electrons can vary among different isotopes of an element, but the number of protons remains constant, defining the element's atomic number. Therefore, the correct answer is the number of protons (Choice B).