The atomic mass of element a is 63.6 atomic mass units. the only naturally occurring isotopes of element a are a-63 and a-65. the percent abundances in a naturally occurring sample of element a are closest to
a) 31% a-63 and 69% -65
b) 69%a-63 and 31% a-65
c) 50% a-63 and 50% a-65
d) 100% a-63 and 0% a-65

Achemistry student needs to standardize a fresh solution of sodium hydroxide. he carefully weighs out of oxalic acid , a diprotic acid that can be purchased inexpensively in high purity, and dissolves it in of distilled water. the student then titrates the oxalic acid solution with his sodium hydroxide solution. when the titration reaches the equivalence point, the student finds he has used of sodium hydroxide solution.calculate the molarity of the student's sodium hydroxide solution. be sure your answer has the correct number of significant digits.