The compound,found in nature in gas phase but ionic in solid state is

Which one of the following pairs of compounds illustrates the law of multiple proportions?

If the angle $\theta$ between the vectors $\overrightarrow{a}=2 x^2 \hat{i}+4 x \hat{j}+\hat{k}$ and $\overrightarrow{b}=7 \hat{i}-2 \hat{j}+x \hat{k}$ is such that $90^{\circ} < \theta < 180^{\circ}$, then $x$ lies in the interval

For a gas,$\frac{R}{C_{V}}=0.4$,where $R$ is the universal gas constant and $C_{V}$ is the molar specific heat at constant volume. The gas is made up of molecules which are

The coefficient of $x^n$ in $\frac{1-2x}{e^x}$ is:

The strength of an acid depends on its tendency to