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:

The universe has trillions of galaxies and counting. Astronomers give names to each galaxy base on its shape (e.i, Sombrero galaxy, Milkyway Galazy, ect,.).
Also, the size of the galaxy is taken into account and their color.