INSTRUCTIONS: Classify each of the following properties of matter as physical [P] or chemical (C). 21. Color
26. Reacts violently with chlorine
22. Density
27. Good conductor of heat
23. Burns easily (flammable)
28. Dissolves readily in water
24. Not affected by acids
29. Melts at 145 °C
25. Boils at 450 °C
30. Malleable

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.