25 mL of 0.1 M lactic acid (CH, CH(OH)COOH) is titrated with 0.1 M sodium hydroxide (NaOH). The titration curve is shown. What is the approximate pKa? At the pKa, what fraction of the carboxyl group will have been converted to COO-? Express your answer as a decimal, not a percent.

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.