When concentrated ${H_2SO_4}$ reacts with $X$ at a temperature of $160-170 \, ^\circ C$,ethylene is obtained. What is $X$?

What are $X$ and $Y$ in the following reactions?

Product $(B)$ is

$A$ body is projected at an angle $\theta$ so that its range is maximum. If $T$ is the time of flight,then the value of maximum range is (acceleration due to gravity $= g$)

$A$ small source of sound moves on a circle as shown in the figure and an observer is standing at $O$. Let $n_1, n_2$ and $n_3$ be the frequencies heard when the source is at $A, B$ and $C$ respectively. Then

In the circuit shown in the figure,the current $I$ is: (in $\,A$)