Question 64 of 66
Q.Which one of the following is used as a standard for atomic mass ?
(a) ^12_6 C
(b) ^12_7 C
(c) ^13_6 C
(d) ^14_6 C
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Start your 14-day free trial to unlock the full solution →This question asks which species serves as the reference standard for the atomic mass scale used in chemistry.
The carbon-12 isotope (^12_6 C) is the internationally accepted standard for atomic mass; one C-12 atom is defined to have a mass of exactly 12 u.
On the modern scale, one atomic mass unit (1 u) is defined as exactly one-twelfth of the mass of a single atom of the carbon-12 isotope. So carbon-12 is assigned a mass of exactly 12 u, and every other atomic and molecular mass is expressed relative to this fixed reference.
Checking the options:
- (a) ^12_6 C — carbon-12, the correct standard (6 protons, 6 neutrons). …
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