When 5ml of HCl was added to the flask, 5 ml of air was
removed. This was done so
that.

A. there was still 140 ml of volume available for the
reaction

B. there was less than atmospheric pressure inside
the flask

C. there was more than atmospheric pressure inside
the flask to drive the reaction

A. There was still 140 ml of volume available for the reaction

Explanation:

According to Avogadro's law, we have that equal volumes of all gases  contains equal number of molecules

According to the ideal gas law, we have;

The pressure exerted by a gas, P = n·R·T/V

Where;

n = The number of moles

T = The temperature of the gas

R = The universal gas constant

V = The volume of the gas

Therefore, given that the volumes and number of moles of the removed air and added HCl are the same, the pressure and therefore, the volume available for the reaction will remain the same

There will still be the same volume available for the reaction.

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.