How many grams of C3H8 are in a 7 L tank at 293 K and 5.45 atm?

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.

b. examine and describe cells

there is none because earth is stationary and flat.

i think it's letter a.