A year is divided into months weeks and days the geologic time scale is also divided into time categories what are the time divisions that are used for the dzialac time scale and what determines how they are divided

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.  

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.