Which of the following statements is true when equilibrium is established in the reaction? $A + B \rightleftharpoons C + D, K_C = 10$

Before any reaction takes place,the value of the reaction quotient $(Q_c)$ is ......

For the reaction $2AB \rightleftharpoons A_2 + B_2$,the equilibrium constant is $49$. What will be the equilibrium constant for the reaction $AB \rightleftharpoons 1/2 A_2 + 1/2 B_2$?

At $T \ K$,the equilibrium constants for the following two reactions are given below:
$2 A_{(g)} \rightleftharpoons B_{(g)} + C_{(g)} ; K_1 = 16$
$2 B_{(g)} + C_{(g)} \rightleftharpoons 2 D_{(g)} ; K_2 = 25$
What is the value of equilibrium constant $(K)$ for the reaction given below at $T \ K$?
$A_{(g)} + \frac{1}{2} B_{(g)} \rightleftharpoons D_{(g)}$

Write the uses of equilibrium constant.

For the reaction $N_2 + 3H_2 \rightleftharpoons 2NH_3$,the equilibrium constant is $k$. What is the equilibrium constant for the reaction $2N_2 + 6H_2 \rightleftharpoons 4NH_3$?