I know 1 mature tree can store 48 lbs CO2 per year and give 260 lbs O2 per tree per year . So exactly how much CO2 1 tree use per year for photosynthesis and storing process or just only 48 lbs ?

I know grassland absorb 2400 – 3600 lbs CO2 per acre per year and create half kilogram O2 per 1 square foot per day . So exactly how much CO2 grassland use per year for photosynthesis and storing process ?

Were do you get those numbers for CO2 and O2 for trees and grass?

The numbers don't tally.

If you take in 48 pounds of CO2 you can't magically turn that into 260Lbs of O2.

Where would the extra 200 odd pounds come from?

 

 

I know 1 mature tree can store 48 lbs CO2 per year and give 260 lbs O2 per tree per year

Trees don't store CO₂ , they store the carbon and (bottom line books) release the the O₂ (when photosynthesizing normally, with respiration damped or swamped). There's twice as many O atoms as C per molecule, and they are each heavier than a C atom. That may clarify your accounting there.

 

The amount of carbon a tree removes from the air varies enormously by species, stage of life, and growing conditions. Also, mode of death - only the carbon sequestered from the atmosphere after death has been actually removed (buried leaves, etc, count, partially. Burned wood does not, completely).

Each molecule of CO2 weighs 44 times as much as a hydrogen atom (it's an odd unit of weight, but it's used a lot in chemistry).

 

Each carbon atom has a mass of 12 on that scale, and each oxygen has a mass of 16.

So 44 grams of CO2 contains 12 grams of carbon and 32 grams of oxygen.

The tree takes that in and splits the C from the O2, it releases the O2 to the air and combines the C with H2O to make (mainly) cellulose.

 

So a tree that takes in 48 lbs of CO2 will produce 48/44 *32 i.e about 34.9 lbs of oxygen.

 

So, as I said, there's about 200 Lbs to still account for (225.1 to be a bit more exact).

 

Where does it come from?