a. #"Number of molecules" = "Avogradro's contant"*"Number of moles"#
#0.45(6.02*10^(23))=2.709*10^(23)~~2.71*10^(23)#
b. #"Number of atoms" = "Number of molecules"*"Number of atoms in one molecule"#
#NH_4Cl# = 6 atoms
#6(2.709*10^(23))=1.6254*10^(24)~~1.63*10^(24)#
c. #"Number of atoms in 1 mole"="Avogadro's constant"*"Number of atoms in one molecule"#
#6(6.02*10^(23))=3.612*10^(24)~~3.61*10^(24)#
d. #"Number of atoms of one element"="Number of molecules"*"Number of atoms of one element in one molecule"#
#4(2.709*10^(23))=1.0836*10^(24)~~1.08*10^(24)#
d. #n(NH_4Cl) = 0.45mol#
#n(H_4)# in #NH_4Cl = 0.45*4/53.5=0.0336448598~~3.36*10^(-2)mol#