Total millimoles of sulphuric acid =60×101=6mmH2SO4
Excess H2SO4≡20×101×21=1mmH2SO4
H2SO4 used in reaction with ammonia =6−1=5mm
Based on the reaction stoichiometry, 2NH3+H2SO4⟶(NH4)2SO4
mm of NH3=10mm
Mass of N=10×10−3×14(moleg)=0.140g