a)

$1.4K+O_2\to 2K_{2}O$

$2.K_{2}O+H_{2}O\to 2KOH$

$3.KOH+HCl{O}_3\to KCl{O}_3+H_{2}O$

$4.KCl{O}_3+HCl\to KCl+HCl{O}_3$

b)

$1.P_4+5O_2\to P_4{O}_{10}$

$2.P_4{O}_{10}+6H_{2}O\to 4H_{3}P{O}_4$

$3.H_{3}P{O}_4+3Ca{\left(OH\right)}_2\to {\left[Ca\left(OH\right)\right]}_{3}P{O}_4+3H_{2}O$

$4.{\left[Ca\left(OH\right)\right]}_{3}P{O}_4+H_{3}P{O}_4\to C{a}_3{\left(P{O}_4\right)}_2+3H_{2}O$

c)

$1.2NO+O_2\to 2N{O}_2$

$2.2N{O}_2+H_{2}O\to HN{O}_2+HN{O}_3$

$3.2HN{O}_3+CuS{O}_4\to Cu{\left(N{O}_3\right)}_2+H_{2}S{O}_4$

$4.Cu{\left(N{O}_3\right)}_2+2NaOH\to Cu{\left(OH\right)}_2+2NaN{O}_3$

d)

$1.S+O_2\to S{O}_2$

$2.2S{O}_2+O_2\to 2S{O}_3$

$3.S{O}_3+H_{2}O\to H_{2}S{O}_4$

$4.H_{2}S{O}_4+KOH\to KHS{O}_4+H_{2}O$

$5.KHS{O}_4+KOH\to K_{2}S{O}_4+H_{2}O$

$6.K_{2}S{O}_4+Pb{\left(N{O}_3\right)}_2\to PbS{O}_4+2KN{O}_3$

e) 

$1.2Ca+O_2\to 2CaO$

$2.CaO+H_{2}O\to Ca{\left(OH\right)}_2$

$3.Ca{\left(OH\right)}_2+HCl\to Ca\left(OH\right)Cl+H_{2}O$

$4.Ca\left(OH\right)Cl+HCl\to CaC{l}_2+H_{2}O$

f)

$1.C+O_2\to C{O}_2$

$2.C{O}_2+H_{2}O+CaC{O}_3\to Ca{\left(HC{O}_3\right)}_2$

$3.Ca{\left(HC{O}_3\right)}_2+Ca{\left(OH\right)}_2\to 2CaC{O}_3+2H_{2}O$

g)

$1.FeC{l}_3+3NaOH\to Fe{\left(OH\right)}_3+3NaCl$

$2.2Fe{\left(OH\right)}_3\stackrel{T}{\to }F{e}_2{O}_3+3H_{2}O$

$3.F{e}_2{O}_3+2Al\to 2Fe+A{l}_2{O}_3$

$4.F{e}_2{O}_3+6HCl\to 2FeC{l}_3+3H_{2}O$

h)

$1.2Al+2NaOH+6H_{2}O\to 2Na\left[Al{\left(OH\right)}_4\right]+3H_2\uparrow$

$2.2Na\left[Al{\left(OH\right)}_4\right]+2HBr\to 2NaBr+2Al{\left(OH\right)}_3+2H_{2}O$

  $3.NaBr+HCl\to NaCl+HBr$  

i)

$1.2Zn+O_2\to 2ZnO$

  $2.ZnO+2KOH+H_{2}O\to K_2\left[Zn{\left(OH\right)}_4\right]$

$3.K_2\left[Zn{\left(OH\right)}_4\right]+4HCl\to ZnC{l}_2+2KCl+4H_{2}O$

j)

$1.C{r}_2{O}_3+6HCl\to 2CrC{l}_3+3H_{2}O$

$2.CrC{l}_3+3NaOH\to Cr{\left(OH\right)}_3\downarrow +3NaCl$

$3.Cr{\left(OH\right)}_3+3NaOH\to N{a}_3\left[Cr{\left(OH\right)}_6\right]$

$4.2Cr{\left(OH\right)}_3\stackrel{T}{\to }C{r}_2{O}_3+3H_{2}O$

$5.2Cr{\left(OH\right)}_3+3H_{2}S{O}_4\to C{r}_2{\left(S{O}_4\right)}_3+6H_{2}O$