What is the principal difference between a strong acid and a weak acid? Strong acids have high concentrations of the hydroxide ion while in solution. When neutralized, strong acids form salt and water while weak acids only form water. Strong acids completely ionize while weak acids only partially ionize. Strong acids are polyprotic while weak acids are monoprotic.

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.

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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.  

since electrons are negative the answer is neagtaive