Which of the following is responsible for the production of biogas?

$A$ big water drop is formed by the combination of $n$ small water drops of equal radii. The ratio of the surface energy of $n$ drops to the surface energy of the big drop is

The magnetic susceptibility of the material of a rod is $499$. Permeability of vacuum is $4 \pi \times 10^{-7} \ H/m$. Absolute permeability of the material of the rod in $H/m$ is:

What is formed when oxalic acid is dehydrated with concentrated $H_2SO_4$?

In which method is recombinant $DNA$ directly injected into the nucleus of an animal cell?