Which observation provided Albert Einstein the clue that he needed to explain the photoelectric effect?

Which observation provided Albert Einstein the clue that he needed to explain the photoelectric effect? Energy of electrons depends on light's frequency, not intensity. A change in which property of light will have no effect on whether or not the photoelectric effect occurs?

Explanation:

Energy of electrons depends on light’s frequency, not intensity.

Explanation:

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.