It's "C" a sample of dust particles at 0 Pascals
atoms are made of 3 types of sub atomic particles; neutrons, protons and electrons
atomic number is the number of protons which is characteristic for the element. Atoms of the same element have the same number of protons.
mass number is the sum of the neutrons and protons.
Isotopes are atoms of the same element with different mass numbers. since they are the same element number of protons are the same but number of neutrons vary.
therefore 2 isotopes are of the same element so they have the same number of protons.
Atomic mass / mass number / atomic weight
(all of which mean the same thing)
It can because Iron is more reactive than Hydrogen and a more reactive metal always replaces a less reactive one in a single replacement reaction