Which element among the alkaline earth metals primarily forms covalent compounds?

Which one of the following graphs represents the Freundlich adsorption isotherm?

Which era is known as the age of birds and mammals?

Let $P$ be a plane passing through the points $(2,1,0), (4,1,1)$ and $(5,0,1)$ and $R$ be any point $(2,1,6)$. Then the image of $R$ in the plane $P$ is

Heterosis is . . . . . . .

An ideal gas expands isothermally from a volume $V_1$ to $V_2$ and then is compressed to the original volume $V_1$ adiabatically. The initial pressure is $P_1$ and the final pressure is $P_3$. The total work done is $W$. Then: