How many neutrons are in an atom with the atomic number of 15 and an atomic mass number of 34? А. A ? 19 B В ? 2 15 C. ? 34

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

what does the table look like