With some value of mixture co and o2 density by hydrogen is 15 . when reaction begun some time later density by hydrogen of the new mixture become 18.75. find volume portion (%) of co2 in the end.

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.

particle   p is an electron and particle q is a neutron