Answer: A. 2
Explanation: The outermost energy level shell is 4s2.
The law of conservation of matter basically states that matter can’t be created or destroyed, only changed in form, so you can rule out any option that mentions destroying or creating matter. That leaves only option A. Atoms cannot be created or destroyed by chemical reactions.
One mole Hydrogen need 1/2mol O_2 .
Moles of Hydrogen
Moles of O_2
Digesting of food because stomaci acid reaction makes things melt w/ enzymes