most of the total mass of a plant comesfrom which source?

Nitrogen
Oxygen
Carbon Dioxide
Water
Hydrogen

Is is carbon dioxide?

2 answers

Water comprises most of our mass too.

Carbon dioxide is one atom of carbon linked to two atoms of oxygen ("di-" means "two").

It is absorbed by plants and exhaled by animals.

I hope this helps. Thanks for asking.
Consider the molecular formula for glucose (other building blocks, such as other sugars, cellulose, and starches are similar ratios)
C6H12O6

Notice there are 6H2O, and 6C

The water is about 1.5 massive as C. So most of the mass comes from water. Other molecules in plants have a similar ratio.