As a musician, you are in the beginning stages of designing a soundproof studio to record your music. Your task is to select a material to line the walls so you have the least amount of echo. Which of the following materials would you choose? A.
Wood because the sound waves will reflect back into the studio as it hits the hard surface.

B.
Wood because the sound waves will be absorbed as they hit the hard surface.

C.
Foam because the sound waves will be absorbed into the foam.

D.
Foam because the sound waves will reflect back into the studio.

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.