Chapter 12, Problem 61GP

To determine

The average density of number of particles in the galaxy, where the most abundant element is atomic hydrogen, considering there are ${10}^{11}$ stars in the galaxy and the size of the galaxy is ${10}^5\text{ light-years}$, where $1\text{ light-year}$ is equal to the distance traveled by the light in $1\text{ year}$ at a speed of $3\times {10}^8\text{ m/s}$. Also, mention the assumptions made about stars.