How potential energy changes when you pull a magnet off a refrigerator door

The potential energy increase.

Explanation:

Potential energy is the energy stored within a physical system. Energy is the ability to do work or cause movement.  A free system acts in the way that minimizes the potential energy, so when you pull a magnet off a refrigerator door you are increasing the potential energy of the system because now if you allow the magnet to move freely, it will snap the door to minimize PE.

answer: c.

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.

            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.