Among the following,which is water insoluble?

In the circuit shown,the energy stored in the $1\,\mu F$ capacitor is ..... $\mu J$.

If the circle $x^2+y^2+8x-4y+c=0$ touches the circle $x^2+y^2+2x+4y-11=0$ externally and cuts the circle $x^2+y^2-6x+8y+k=0$ orthogonally,then $k$ is equal to

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

If $\vec{P} \cdot \vec{Q} = PQ$,then the angle between $\vec{P}$ and $\vec{Q}$ is ............. $^\circ$.