Question

If the light is both wave and particle ..

then when light is said to be wave and when it is said to be particle ?​

Answer 1

Consider electrons incident on a Young's double slit

If one slit is covered, the electrons will form a maximum, on the screen, as if they were particles incident on the screen

If both slits are open, the pattern formed on the screen will be the same as if a wave were incident on the screen, even tho electrons are slowed to the point that only 1 electron is incident on the screen at one time.

That means that the electron interferes with itself to create the interference pattern on the screen, and there is no way to determine which slit the electron went thru without destroying the interference pattern.