Which of the following substances has a molar mass of 208g

Missing question: P₂O₅, BaCl₂, AlCl₃, MgCl₂.
Answer is: barium chloride (BaCl₂).
a) M(P₂O₅) = 2 · Ar(P) + 5 · Ar(O) · g/mol.
M(P₂O₅) = 2 · 31 + 5 · 16 · g/mol = 142 g/mol.
b) M(BaCl₂) = Ar(Ba) + 2 · Ar(Cl) · g/mol.
M(BaCl₂) = 137,3 + 2 · 35,45 · g/mol = 208,2 g/mol.
c) M(AlCl₃) = Ar(Al) + 3 · Ar(Cl).
M(AlCl₃) = 27 + 3 · 35,45 · g/mol = 133,35 g/mol.
d) M(MgCl₂) = Ar(Mg) + 2 · Ar(Cl) · g/mol.
M(MgCl₂) = 24,3 + 2 · 35,45 · g/mol = 95,2 g/mol.

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