Answer:
i)20369 photons
ii) 40 ps
Explanation:
Momentum of one Sodium atom:

In other to stop it, it must absorb the same momentum in photons:

Now, for the minimun time, we use the speed of light and the wavelength. For the n photons:

Answer:
State A = piece of metal; State B = air
Explanation:
For the three main states of matter here's how it breaks down.
Solid - Cannot be compressed and retains its shape
Liquid - Cannot be compressed and does not retain its shape
Gas - Compressible and does not retain its shape.
Knowing this State A has to be solid. Only one of the options has A as a solid, so that's the answer. Worth knowing state B is a gas though, only one compressible, just like solid is the only one that retains its shape.
The property of matter that is responsible for electrical phenomena, existing in a positive or negative form.
Its called static friction.