The answer is B. making sawdust.
Because, to make sawdust you have to shred wood and you can't reverse that. Therefore, making sawdust is irreversible.
The unified cell theory states that: all living things are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells.
7 protons means that N atom has 7 electrons
1st level can have only 2 e⁻, and we have left over of 7-2=5 e⁻, that will go on the second level.
B. 2,5
CH4 as empirical formula is the simplest ratio of all the atoms in a molecule
I know that one is oxygen. I dont know the other.