Sometimes on especially hot days, a wooden door, that opens and closes just fine during cooler months, will be hard to open and close. Why is the door hard to open and close on hot days? Hint:Think about the difference in the spacing of molecules in solids that are heated and cooled. please help, I wanna finish this quickly and pick up my grade, tysm if u do help!

11 players on a field that has a maximum of 11 players

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.