Ammonia with excess of $Cl_2$ forms:

If in a $\triangle ABC$,$\frac{1}{a+c} + \frac{1}{b+c} = \frac{3}{a+b+c}$,then $\angle C$ is equal to (in $^{\circ}$)

In a compound,$C, H,$ and $N$ atoms are present in the ratio $9 : 1 : 3.5$ by weight. If the molecular weight of the compound is $108$,what is its molecular formula?

Which of the following is a linear molecule?

Let $n(U) = 700, n(A) = 200, n(B) = 300$ and $n(A \cap B) = 100,$ then $n(A^c \cap B^c) = $