Which of these statements is true?
a. some molecules may contain no atoms.
b. some elements found in nature exist as molecules.
c. some compounds include only one type of element.
d. some atoms are made of two or more different elements.

Insoluble sulfide compounds are generally black in color. which of the following combinations could yield a black precipitate? check all that apply. na2s(aq)+kcl(aq) li2s(aq)+pb(no3)2(aq) pb(clo3)2(aq)+nano3(aq) agno3(aq)+kcl(aq) k2s(aq)+sn(no3)4(aq)