Do anyone know the answer?

C2H4 + 3O2 --> 2CO2 + 2H2O

Explanation:

For an equation to be balanced, it must have an equal number of atoms on each side. C2H4 + 3O2 --> 2CO2 + 2H2O is the only equation out of these four the fulfills this requirement.

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.