Why is it not possible to see an atom with naked eyes?

is it possible to open a pen cap with one finger? Why?

Why it is not possible to determine the absolute value of potential of a single electrode?

Why it is not possible to measure the voltage of an isolated reduction half reaction or the potential of a single electrode?

Why is it possible to write on rough blackboard with chalk ?

Is it possible to have an elements with atomic number 1.5 placed between hydrogen and helium?

Why preparation of aryl halide is not possible by reaction of phenol with PCl_3 ?

why is short wave communication over long distance not possible by surface wave propagation ?

Why is a normal eye not able to see clearly the objects placed closer than 25 cm?