Atomic and Molecular Masses NEET Questions

Physical Chemistry - Some Basic Concepts of Chemistry

Atomic and Molecular Masses MCQ Questions


7.
The atomic mass shown in the periodic table for most elements is:
A.
The mass of the most stable isotope
B.
The average atomic mass weighted by isotopic abundance
C.
The mass of the most abundant isotope only
D.
The arithmetic mean of all isotopic masses
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ANSWER :
B. The average atomic mass weighted by isotopic abundance
8.
Carbon has two main natural isotopes: ¹²C (98.892%) and ¹³C (1.108%). The average atomic mass of carbon is:
A.
12.011 u
B.
12.500 u
C.
13.000 u
D.
12.000 u
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ANSWER :
A. 12.011 u
9.
Chlorine exists as two isotopes ³⁵Cl (75.77%, mass 34.9689) and ³⁷Cl (24.23%, mass 36.9659). The average atomic mass of chlorine is approximately:
A.
35.0
B.
36.0
C.
35.5
D.
37.0
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ANSWER :
C. 35.5
10.
If an element X has two isotopes ⁶⁹X (60%) and ⁷¹X (40%), the average atomic mass of X is:
A.
69.4
B.
70.2
C.
69.0
D.
69.8
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ANSWER :
D. 69.8
11.
Boron has two isotopes ¹⁰B (mass 10.013) and ¹¹B (mass 11.009). If the average atomic mass of boron is 10.811, the percentage abundance of ¹⁰B is approximately:
A.
20%
B.
30%
C.
80%
D.
70%
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ANSWER :
A. 20%
12.
Magnesium has three isotopes: ²⁴Mg (78.99%, mass 23.985), ²⁵Mg (10.00%, mass 24.986), and ²⁶Mg (11.01%, mass 25.983). The average atomic mass is approximately:
A.
24.31
B.
24.99
C.
23.99
D.
25.31
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ANSWER :
A. 24.31