Please help! I need answers please!
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