Ineed answers !
2. the discovery of what element showed the usefulness of mendeleev’s periodic table?

a: gallium
b: aluminum
c: scandium
d: germanium

3. why is not a reason why the mass of an atom is expressed in atomic mass units rather than in grams?

a: atomic mass allows for mass differences in isotopes.
b: atomic mass units make it easier to compare the masses of atoms.
c: the mass in grams is too small to be useful.
d: scientists could not agree on a standard.

4. what class of elements includes all of the elements that are gases at room temperature?

a: metals
b: nonmetals
c: metaloids