A-
i) [tex]PbCl_2 + 2AgNO_3 = 2AgCl + Pb(NO_3)2[/tex]
ii) [tex]AlCl_3 + 3NH_4OH = Al(OH)_3 + 3NH_4Cl[/tex]
iii) [tex]2FeCl_3 + 3Ca(OH)_2 = 3CaCl_2 + 2Fe(OH)_3[/tex]
iv) [tex]Pb(ClO_3)_2 + K_2SO_4 = PbSO_4 + 2KClO_3[/tex]
v) [tex]2Na + 2HOH = 2NaOH + H_2[/tex]
vi) [tex]Zn + 2HCl = ZnCl_2 + H_2[/tex]
vii) [tex]Al + 3AgCH_3COO = Al(CH_3COO)_3 + 3Ag[/tex]
viii) [tex]MgO + 2HNO_3 = Mg(NO_3)_2 + H_2O[/tex]
ix) [tex]3MnO_2 = Mn_3O_4 + O_2[/tex]
B- Because chemical formula has its own unique set of elements and subscripts
Hope this Helps :)