Please help! I need answers please!

1. The discovery of what element showed the usefulness of Mendeleev’s periodic table?
   
   

A: gallium

B: aluminum

C: scandium

D: germanium

1. 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.

1. What class of elements includes all of the elements that are gases at room temperature?
   
   

A: Metals

B: Nonmetals

C: Metaloids