Element x is found in two forms: 90.0% is an isotope that has a mass of 20.0, and 10.0% is an isotope that has a mass of 22.0. what is the atomic mass of element x?
a. 20.0
b. 20.2
c. 20.8
d. 21.2
e. 21.8
can anyone explain this one for me?

Why does a red shoe appear red in daylight

Which of the following is not a good technique for managing used oil? a) have specific, labeled catch pans available for technicians who are collecting oil b) spills in your shop and any releases on pavement or outside should be poured down a drain c) do not use oil containers for antifreeze or other non-similar fluids d) be prepared for oil spills with the proper absorbents

Areaction is first order with respect to reactant x and second order with respect to reactant y. which statement describes the rate law for this reaction?