The material, Brass is not an element. The different elements can be seen on the periodic table. Anyway, brass is an alloy of metal. Although, gold, silver, copper and many others are elements. Hope i helped. Have a nice day.
Answer:
hydrogen atom but see the note below.
Explanation:
This is either the most common hydrogen ion or a hydrogen atom. It cannot be either of hydrogen's isotopes.
Given :
Molarity of acetic acid solution, M = 0.10 M.
pKa of acetic acid, pKa = 4.75 .
To Find :
Percentage dissociation of 0.10 M solution of acetic acid.
Solution :
We know, 
Taking antilog both side, we get :

Since, acetic acid has 1 hydrogen atom to loose , so it is a monoprotic acid.
Now, percentage dissociation of monoprotic acid is given by :

Hence, this is the required solution.
A positive solid sphere with electrons dispersed.
C of course is the correct