Multiple Choice
Which one of the following elements does not exist as a diatomic molecule in nature?
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2. Atoms & Elements
Periodic Table: Elemental Forms
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Which of the following formulas represents an element in its natural state at standard conditions?
A
CO_2
B
H_2O
C
NaCl
D
O_2
Verified step by step guidance1
Understand that an element in its natural state at standard conditions (25°C and 1 atm) exists as the pure substance composed of only one type of atom or molecule, not combined with other elements in a compound.
Review each formula given: CO_2 (carbon dioxide) is a compound made of carbon and oxygen; H_2O (water) is a compound made of hydrogen and oxygen; NaCl (table salt) is a compound made of sodium and chlorine.
Recognize that O_2 (oxygen gas) is a diatomic molecule consisting of two oxygen atoms bonded together, which is how oxygen naturally exists in the atmosphere under standard conditions.
Conclude that among the options, only O_2 represents an element in its natural state at standard conditions because it is a pure elemental form, not a compound.
Remember that elements can exist as single atoms (like noble gases) or as molecules made of the same atoms (like O_2, N_2) in their natural state.
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