The mass number tells the total number of and nucleus of an atom. These particles collectively are called since both are located in the nucleus.

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.

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explanation:

i don't see a text, but i am gonna assume this *orbit* the curved path, usually elliptical, described by a planet, satellite, spaceship, etc., around a celestial body, as the sun.

fe 55.85 g/mol and h2o 18.02 g/mol.