Which of the following is the smallest size grain that can be seen using a normal microscope using visible light $(400 \ nm < \lambda < 700 \ nm)$ (in $nm$)?

Two parallel pillars are $11 \, km$ away from an observer. The minimum distance between the pillars so that they can be seen separately will be.....$m$

The human eye has an approximate angular resolution of $\theta = 5.8 \times 10^{-4} \text{ rad}$ and a typical photo printer prints a minimum of $300 \text{ dpi}$ (dots per inch, $1 \text{ inch} = 2.54 \text{ cm}$). At what minimal distance $d$ should a printed page be held so that one does not see the individual dots (in $\text{ cm}$)?

Two points separated by $0.05 \, mm$ can just be inspected in a microscope when light of wavelength $6000 \, \mathring{A}$ is used. If light of wavelength $3000 \, \mathring{A}$ is used,then the limit of resolution becomes ........... $mm$.

The diameter of the objective of a telescope is $3.6 \ m$. The limit of resolution of the telescope for a light of wavelength $540 \ nm$ is

The diameter of the objective of a telescope is $1 \ m$. Its resolving limit for light of wavelength $4538 \ \text{Å}$ will be: