4) Which indicator, when added to a solution, changes color from yellow to blue as the pH of the
solution is changed from 5.5 to 8.0?
a bromcresol green
b) Litmus
c) bromthymol blue
d) methyl orange

c) bromthymol blue

Explanation:

An acidic solution has a pH value less than 7, while the pH is 7 for a neutral solution and grater than 7 for a basic solution.

Bromothymol blue is a pH indicator which is yellow in color when placed in an acid (pH under 7), the color is green in a neutral solution (pH of 7) and blue in an basic solution (pH over 7).

If bromthymol blue is added to a solution with an initial pH of 5.5 (acidic), the color would be yellow and as the pH changes to 8 (basic), the color changes to blue.

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.  

i think   the answer is c hope i'm right