a. The atomic mass defines the elemental identity of an atom. b. The atomic number of an element is approximately equal to the number of protons in an atom of that element. c. Helium is the smallest atom and has an atomic number of 1. d. Isotopes of the same element have the same atomic mass.

B

Explanation:

option b is correct because

hydrogen is smallest atom

isotopes of elements have different atomic mass

atom mass have nothing to do with elemental identity

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.