4. Given that a sample of air is made up of nitrogen, oxygen and argon in the mole fractions 78% N2, 21% O2 and 1.0% Ar, the density of air at standard temperature and pressure is mg/L.
(A) 1.26 × 104
(B) 12.6 × 10-1
(C)1.26 × 101
(D) 1.3 × 102
(E)1.3 × 103
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