How to make a balance equation?

To balance a chemical equation, start by writing down the number of atoms in each element, which is listed in the subscript next to each atom. Then, add coefficients to the atoms on each side of the equation to balance them with the same atoms on the other side.

answer; i believe the correct answer is (c) /// is a homogeneous mixture of gaseous substance nitrogen,oxygen and smaller amounts of other substancesmixtures can be either ( homogeneous or heterogeneous)plz check first good luck

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.