How can one determine the median of a data set?
by ordering the data points and finding the middle value of the set
by ordering the data points and finding the most common value in the set
by finding the average of the different values in the set
by finding the difference between the highest and lowest values of the set

by ordering the data points and finding the middle value of the set

Explanation:

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.