Law of conservation of mass states that all chemicals equations have to be balanced . true false

True

Explanation:

Law of conservation of mass states that for a closed system the mass have to remain constant in time, so for chemical equations you need to ensure that is balanced. Otherwise if you do not balance the equation you would not know how much of a compound to weight for a certain reaction, or you weight an incorrect quantity.

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.

qualitative observation deals with data that can be observed with our senses: sight, smell, touch, taste, and hearing. they do not involve measurements or numbers. for instance, colors, shapes, and textures of objects are all qualitative observations.