Na (atomic no. 11) reacts with Cl (atomic no. 17) to become stable. In the reaction, Na will , while Cl will .

Sodium will an electron and chlorine will gain an electron

Explanation:

The electronic configurations of sodium and chlorine are;

Sodium- 1s2 2s2 2p6 3s1

Chlorine- 1s2 2s2 2p6 3s2 3p5

Hence, sodium can easily loose one electron to chlorine to attain a noble gas configuration while chlorine accepts one electron to attain the noble gas configuration.

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.