Question

On Earth, naturally occurring calcium metal contains 6 isotopes: Ca-40, Ca-42, Ca-43, Ca-44, Ca-46, Ca-48. Select all of the following that are true for a sample of naturally occurring calcium.
A) The average mass of the calcium atoms is 40.078 amu.
B)One mole of Ca-40 has a mass of 40.078 grams.
C)All of the calcium atoms have an atomic number of 20.
D)All of the calcium atoms have a mass number of 40.078
E) Some of the calcium atoms have a mass number of 40.
F)Some of the calcium atoms have a mass of exactly 42 amu.
G) One mole of the calcium atoms will have a mass of 40.078 amu.
H) It is likely that the most abundant isotope is Ca-40.
I chose A,B,C,E,G,H and can't figure out which ones I chose wrong. Thanks!

Answer 1

A is probably right but I don't there there is enough information there to know that. You must go to a periodic table to check it out.
I don't think B is right. The average of all of the isotopes is 40.078 but Ca-40 is not that mass.
C is ok.
D is not right. D would be ok if they said mass but not mass NUMBER. Mass number is the NUMBER of protons + NUMBER neutrons.
E is ok.
F is not right
G could be right but with no percentages given who knows. If you're given the periodic table you know it is right.
H probably is right but there isn't enough information in H to make sure; i.e., I know the atomic mass Ca is 40.078 which means most of the metal probably is 40, especially since there is no 41.