Q. Elements A, B and C occur as Dobereiners triads. If the atomic mass of A is 7 and that of C is 39, what will be the atomic mass of B?
A) 40
B) 20
C) 12
D) 23
✔ Correct Answer: 20
Exam Insight
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A) 40
B) 20
C) 12
D) 23
✔ Correct Answer: 20
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