Can someone help me with these two chemistry problems?

Question

I'm having trouble with them and idk what to do

 

2. A student has identified a material as a mixture. What is the minimum number of distinct substances that the student has detected in the material?

 

6. An element has three naturally occurring isotopes. The relative abundances of the isotopes are 0.27%, 9.25%, and 90.48%. The most abundant isotope has an atomic mass of 19.99amu. The least abundant isotope has an atomic mass of 20.99amu, and the remaining isotope has an atomic mass of 21.99amu

Answer 1

For the first question: A student has identified a material a mixture and how many unique components are detected in the material. To be a mixture it has to have more than one unique component, so the minimum has to be at two.

 

The second question got cut off, but I will assume it means to calculate the average atomic weight.

 

Average Atomic Mass= (mass 1 * abundance 1) + (mass 2 * abundance 2) + (mass 3 * abundance 3)

 

Avg Atomic Mass= (19.99 amu * (90.48/100)) + (21.99 amu * (9.25/100)) + (20.99 amu * (0.27/100))

 

From there it is just plugging in the numbers and using the correct number of significant figures.