isotope percent abundance

Rubidium has two common isotopes, ⁸⁵Rb and ⁸⁷Rb. If the abundance of ⁸⁵Rb is 72.2% and the abundance of ⁸⁷Rb is 27.8%, what is the average atomic mass of rubidium?

• 85.468 amu

• 37 amu

• 85.6 amu

• 86.4 amu

There are two primary isotopes found in any sample of copper: copper-63 and copper-65. The isotope ⁶⁵Cu composes 69.2% of the sample and ⁶³Cu comprises the other 30.8%. Based on this data, what is the atomic mass of copper?

• 29 amu

• 63.546 amu

• 64.4 amu

• 63.6 amu

Magnesium consists of three naturally occurring isotopes. The percent abundance of  these isotopes is as follows: ²⁴Mg (78.70%), ²⁵Mg (10.13%), and ²⁶Mg (11.7%). The average atomic mass of the three isotopes is 24.3050 amu. If the atomic mass of ²⁵Mg is 24.98584 amu, and ²⁶Mg is 25.98259 amu, calculate the actual atomic mass of ²⁴Mg.  

• 23.985 amu
• 21.421 amu
• 24.463 amu
• 24.002 amu

How many neutrons does an atom of the isotope Neon-22 have?

• 12
• 10
• 22
• 20

Four isotopes of lead include lead-204, lead-206, lead-207, and lead-208.  The average atomic mass of lead is 207.2.  Which isotope of lead is likely to be the most abundant.

• 204
• 206
• 207
• 208