純凈物硫酸銨中氮元素的質(zhì)量分?jǐn)?shù)=

28

132

×100%=21.2%
A、CO（NH₂）₂中氮元素的質(zhì)量分?jǐn)?shù)=

28

60

×100%=46.7%
B、NH₄HCO₃中氮元素的質(zhì)量分?jǐn)?shù)=

14

79

×100%=17.8%
C、NH₄NO₃中氮元素的質(zhì)量分?jǐn)?shù)=

28

80

×100%=35%
D、NH₄Cl中氮元素的質(zhì)量分?jǐn)?shù)=

18

53.5

×100%=26.2%
硫酸銨樣品含氮量為19%＜21.2%，則雜質(zhì)中氮的質(zhì)量分?jǐn)?shù)必然低于硫酸銨樣品中的含氮量19%，
故選：B．