$Na + C + N \rightarrow NaCN$

$6 NaCN + FeSO _4 \rightarrow Na _4\left[ Fe ( CN )_6\right]+ Na _2 SO _4$

$Na _4\left[ Fe ( CN )_6\right]+ Fe ^{3+} \rightarrow Fe _4\left[ Fe ( CN )_6\right]_3$

(Prussian blue)

Sulphur detection by Sodium nitroprusside

$Na _2\left[ Fe ( CN )_5 NO \right]+ Na _2 S \rightarrow  Na 4\left[ Fe ( CN )_5 NOS \right]$

$\text { [Purple }]$

Phosphorus detection by ammonium molybdate

$Na _3 PO _4+3 HNO _3 \rightarrow H _3 PO _4+3 NaNO _3$

$H _3 PO _4+12\left( NH _4\right)_2 MoO _4+21 HNO _3 \rightarrow$

$\left( NH _4\right)_3 PO _4 .12 MoO _3+21 NH _4 NO _3+12 H _2 O$

$\text { (canary yellow) }$

$\text { Halogen give specific coloured ppt with }$

$AgNO _3( aq )$

$NaCl + AgNO _3( aq ) \rightarrow AgCl + NaNO _3$

$\text { (White) }$

$NaBr + AgNO _3( aq ) \rightarrow AgBr + NaNO _3$

$\text { (Pale yellow) }$

$NaI + AgNO _3( aq ) \rightarrow AgI + NaNO _3$

$\text { (Yellow) }$