a) mNH3=14u+3*1u=17 u
b) mSO3=32u+3*16u=80 u
c) mCH4=12u+4*1u=16 u
d) mNaOH=23u+16u+1u=40 u
e) mK2SO4=2*39u+32u+4*16u=174 u
f) m Ba(OH)2=137u+2*16u+2*1u=171 u