As a box is sliding down a ramp, a 10-n force of gravity is pulling the box down the ramp while a 2-n force of friction acts to stop the box. what is the net force accelerating the box down the ramp?

the first point, i am pretty sure.

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.