Multiple Choice
Which part of the periodic table indicates the number of energy levels (principal energy shells) in the electron cloud of an atom?
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2. Atoms & Elements
Periodic Table: Phases
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Which of the following elements is a liquid at room temperature and normal atmospheric pressure?
A
Sodium (Na)
B
Oxygen (O2)
C
Mercury (Hg)
D
Chlorine (Cl2)
Verified step by step guidance1
Understand the question: It asks which element is a liquid at room temperature (about 25°C) and normal atmospheric pressure (1 atm).
Recall the physical states of the given elements at room temperature: Sodium (Na) is a solid metal, Oxygen (O_2) is a gas, Mercury (Hg) is a metal that is liquid, and Chlorine (Cl_2) is a gas.
Remember that most elements are solids or gases at room temperature, with very few exceptions being liquids.
Identify Mercury (Hg) as the only metal that is liquid at room temperature and atmospheric pressure due to its low melting point (about -38.83°C).
Conclude that Mercury (Hg) is the correct answer because it uniquely exists as a liquid under these conditions.
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