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Homework Practice

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Atoms and Molecules: From Particles to Formulae

Section A: Core Ideas

Question 1mcq
Which option correctly identifies oxygen gas, O2O_2?
A.An atom of a compound
B.An ion of a salt
C.A molecule of an element
D.A molecule of an ionic compound
Question 2mcq
Which substance is a molecule of an element?
A.CO2CO_2
B.H2OH_2O
C.NaClNaCl
D.N2N_2
Question 3mcq
Which property is commonly associated with ionic compounds such as sodium chloride?
A.They are made of oppositely charged ions.
B.They are always made of single neutral atoms.
C.They never dissolve in water.
D.They contain only molecules of one element.
Question 4mcq
Which ion is a cation?
A.Cl−Cl^-
B.Na+Na^+
C.O2−O^{2-}
D.SO42−SO_4^{2-}
Question 5mcq
An atom has electronic configuration 2,8,12,8,1. Which ion is it most likely to form?
A.−1-1 ion
B.+3+3 ion
C.+1+1 ion
D.Neutral molecule only

Section B: Application Practice

Question 6mcq
What is the correct formula of magnesium chloride if magnesium has valency 2 and chlorine has valency 1?
A.Mg2ClMg_2Cl
B.MgClMgCl
C.Mg2Cl2Mg_2Cl_2
D.MgCl2MgCl_2
Question 7mcq
Which formula uses the correct convention for water?
A.H2OH_2O
B.h2oh2o
C.HO2HO2
D.H(2)OH(2)O
Question 8mcq
Which pair is correctly matched?
A.HeHe — molecule of a compound
B.NaClNaCl — compound
C.O2O_2 — atom of a compound
D.H2OH_2O — element
Question 9mcq
Which substance is best described as a covalent compound molecule?
A.O2O_2
B.NaClNaCl
C.CH4CH_4
D.ArAr
Question 10mcq
Which pair is most likely to form an ionic compound?
A.Carbon and hydrogen
B.Oxygen and oxygen
C.Nitrogen and nitrogen
D.Sodium and chlorine