14. ____secl₆ + ____o₂ → ____seo₂ + ____cl₂

Explanation:

Step1: Balance Se atoms

The number of Se atoms on both sides of the equation must be equal. Currently, there is 1 Se in $SeCl_6$ and 1 Se in $SeO_2$. So the coefficient of $SeCl_6$ and $SeO_2$ can be set to 1 for now. $1SeCl_6 + O_2\rightarrow1SeO_2+Cl_2$

Step2: Balance Cl atoms

In $SeCl_6$, there are 6 Cl atoms. In $Cl_2$, to balance the Cl - atoms, since each $Cl_2$ molecule has 2 Cl atoms, the coefficient of $Cl_2$ should be 3. $1SeCl_6 + O_2\rightarrow1SeO_2 + 3Cl_2$

Step3: Balance O atoms

In $SeO_2$, there are 2 O atoms. In $O_2$, to get 2 O atoms on the left - hand side, the coefficient of $O_2$ should be 1. $1SeCl_6+1O_2\rightarrow1SeO_2 + 3Cl_2$

Answer:

$1SeCl_6+1O_2\rightarrow1SeO_2 + 3Cl_2$