What is required in order to determine whether or not an object moves

. a reference point is required to determine whether or not an object moves

Explanation:

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.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements