Which among the following compounds has the highest boiling point?

The network shown in the figure is a part of a complete circuit. If at a certain instant the current $i$ is $5 \ A$ and is decreasing at the rate of $10^3 \ A/s$,then $V_A - V_B$ is ..... $V$.

If $\frac{(1+i) x-i}{2+i}+\frac{(1+2 i) y+i}{2-i}=1$,then $(x, y)$ is equal to

Which of the following elements shows polymorphism?

In the arrangement shown in the figure,the ends $P$ and $Q$ of an unstretchable string move downwards with a uniform speed $U$. Pulleys $A$ and $B$ are fixed. The mass $M$ moves upwards with a speed:

In the adjoining circuit,the battery $E_1$ has an emf of $12 \, V$ and zero internal resistance,while the battery $E_2$ has an emf of $2 \, V$. If the galvanometer $G$ reads zero,then the value of the resistance $X$ (in $\Omega$) is