In which group of organisms do the cell walls form two thin overlapping shells that fit together?

$A$ metal crystallises in a face-centred cubic $(FCC)$ structure. If the edge length of its unit cell is '$a$',the closest approach between two atoms in the metallic crystal will be:

If the work done in blowing a bubble of volume $V$ is $W$,then the work done in blowing the bubble of volume $2V$ from the same soap solution will be

$A$ ray of light is incident on the hypotenuse of a right-angled prism after travelling parallel to the base inside the prism. If $\mu$ is the refractive index of the material of the prism,the maximum value of the base angle for which light is totally reflected from the hypotenuse is

Which part of the world has a high density of organisms?

Which semi-dwarf variety of plant was developed by Nobel laureate Norman $E$. Borlaug?