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PHY 104 PHY 104 Past Questions Objective Question
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Question

What is the atomic weight of a hypothetical element consisting of two isotopes, one with mass = 64.23 amu (26.0%), and one with mass = 65.32 amu?
Options
A 65.3 amu
B 64.4 amu
C 64.9 amu
Correct Answer
D 65.0 amu
Correct Answer

Option C is the correct answer.

Detailed Explanation

The atomic weight is the weighted average. The first isotope has abundance 26.0% (0.26), and the second must have 74.0% (0.74). Atomic weight = 64.23(0.26) + 65.32(0.74) = 16.6998 + 48.3368 = 65.0366 amu. This is closest to 65.0 amu (Option D). Let's recheck. 64.230.26 = 16.70. 65.320.74 = 48.34. Sum = 65.04 amu. Option D (65.0 amu) is the closest.

Hint

Atomic weight is the weighted average based on the relative abundances of the isotopes.

Question Info

Course: PHY 104
Topic: PHY 104 Past Questions
Type: Objective
Difficulty: Not specified
Question 772 of 947
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