Answer : The correct expression will be:

Explanation :
The chemical reactions are :
(1)

(2)

The final chemical reaction is :

Now we have to calculate the value of
for the final reaction.
Now equation 1 is multiply by 2 and then add both the reaction we get the value of 'K'.
If the equation is multiplied by a factor of '2', the equilibrium constant will be the square of the equilibrium constant of initial reaction.
If the two equations are added then equilibrium constant will be multiplied.
Thus, the value of 'K' will be:

The value of "d" is 80°
Explanation:
Cyclic quadrilaterals are the special group of quadrilaterals with all its base lying on the circumference of the circle. In other words, a quadrilateral inscribed in a circle is called a cyclic quadrilateral.
Cyclic quadrilateral are characterised by some special features such as
- Sum of opposite angles of a cyclic quadrilateral is always a supplementary angle.
- If one of the sides of a cyclic quadrilateral is produced, then the exterior angle so formed is always double of the corresponding interior angle.
Using the property 1
We find that since the quadrilateral is cyclic, opposite pairs must be supplementary
100°
+∠D must be equal to 180°
D=180°
-100°
=80°