Question

the periodic table unit test
which statement best explains why hydrogens atomic number is equal to its mass? (1 point)
o hydrogen does not have any neutrons
o hydrogen only has one electron
o hydrogen is in the first row and the first column of the periodic table
o hydrogen is stable, with two electrons in its outer shell

Explanation:

The atomic number of an element is the number of protons in its nucleus. The mass number is the sum of protons and neutrons. For hydrogen, if it has no neutrons (as in the most common isotope, protium), then mass number = number of protons (atomic number). The other options are not relevant to the relationship between atomic number and mass number. Option 2 (only one electron) relates to atomic number (since in a neutral atom, number of electrons = number of protons) but doesn't explain the mass - number equality. Option 3 (position in periodic table) is just a fact of its placement and not the reason for mass - atomic number equality. Option 4 is incorrect as hydrogen in its normal state (not as a hydride ion) has 1 electron in its outer shell (and even if considering stability, it doesn't explain the mass - atomic number relationship).

Answer:

Hydrogen does not have any neutrons.