If`N_(1),N_(2),N_(3),……`are the number of molcules with molecular masses `M_(1),M_(2),(M_(3),…`respectively ,then mass average molar mass is expressed as:
A. `(N_(1)M_(1)^(2),N_(2)M_(2)^(2),+……)/((N_(1)M_(1),N_(2)M_(2),+……))=(SigmaNiMi^(2))/(SigmaNiMi)`
B. `(N_(1)M_(1),N_(2)M_(2),+……)/((N_(1),N_(2),+……))=(SigmaNiMi)/(SigmaNi)`
C. `(SigmaMi^(2))/(SigmaNi)`
D. `(SigmaNiMi)/(SigmaMi)`
