Atomic mass number is the number of protons and neutrons. Subtract 80-35=45 is the number of protons. Because the atom is neutrally charged, the number of protons must equal the number of electrons, so there are 45 electrons.
Sodium is a metal and bromine is a nonmetal so they form an ionic compound
nonmetals and nonmetals form covalent compounds
4. A
because PbCl2 is an ionic compound and it's solid, so it's a substance.
It cannot be mixture, because it's a pure molecule.
5. D
despite that both substances are gases, colorless they are different molecules, so they should have different either chemical and physical properties
6. C
this substance made from W atoms and others are made from molecules
Just like how heat moves from a region of higher
temperature to a region of lower temperature, molecules also tend to move from
a region of higher concentration to a region of lower concentration. This is
called natural diffusion and is naturally happening to reach stability.
