Correct Answer - C

The given equation can be shown as

Rate of flow of heat will be equal in both the slabs

`therefore (12-x)K_(1)= K_(2) (x-0)`

`12-x = 2x rArr x=4^(@)`C `(therefore K_(1) = (K_(2)/2)`

The temperature difference across slab

`A = (12-x) = (12-4) = 8^(@)`C