The correct choice is
D. 22 Hz and 42 Hz.
In fact, the beat frequency is given by the difference between the frequencies of the two waves:
In this problem, the beat frequency is 
, therefore the only pair of frequencies that gives a difference equal to 20 Hz is
D. 22 Hz and 42 Hz.
Find refractive index first
Now
I can't see that cube from here.
But if the length of the side of the cube is ' K ' units,
then the surface area of the cube is 6K² units², and
the volume of the cube is K³ units³.
The ratio of the surface area to the volume is
(6K² units²) / (K³ units³) = (6) / (K units) .
So for example, if the side of the cube is 2 inches, then
the ratio of surface area to volume is "3 per inch".
That's the answer. I did the whole thing in order to earn
the points, but I don't expect you to understand much of it,
because I see from your username that you suck at math.
I'm sorry you decided that. Now that you've put up the
brick wall, it'll be even harder for any math to find its way
in there, and you'll miss out on a lot of the fun.
Answer: the particles are more orderly in region 1
Explanation: region 1 is when the substance is a solid and as it is heated the particles move further apart and have more kinetic energy.
