(b) Define, in terms of oxidation state, the Oxidizing agent a substance which gains oxygen
a substance whis lose hydrogen
a substance which experiences a decrease in oxidation state
a substance which experiences an increase in oxidation state

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.

what is the question here. i think you messed up.