Why is `MgCl_(2)` molecule linear whereas the molecules of `SnCl_(2)` chloride has angulare shape ?

Explanation

Let us find the hybridisation of central atom in both these molecules.
In `MgCl_(2),` hybridisation of Mg =1/2[4+2-0+0]=4/2=2(sp)
In `SnCl_(2),` hybridissartion of Sn = 1/2[4+2-0+0]=6/2=3 `(sp^(2))`
Thus , `MgCl_(2)` is linear while `SnCl_(2)` is expected to have planar geometry. However, the presence of a lone pair elecrtrons on Sn atom makes it angular.