Question

Which of the following is the standard for the atomic mass?
A. $_1^1H$
B.$_6^{12}C$
C. $_6^{14}C$
D. $_8^{16}C$

Answer 1

Atomic mass is a unit that is used by scientists to do the measurements of mass of particles with atomic sizes. A unit is considered as a standard so as to define quantities universally in order to avoid confusion and to have uniformity. It is defined specifically with respect to the sixth element of the periodic table.

Complete step by step answer:
-The standard for the atomic mass is defined as a mass exactly equal to one-twelfth the mass of one carbon-12 atom. It is generally used to express the mass of atomic and subatomic particles because the atomic mass of an atom is very small as we know that atoms are so small that they can’t be broken down further into small pieces.
-In earlier times, scientists used to determine the mass of one atom with respect to another atom with the help of experiments. But nowadays, it has been standardised and abbreviated as ‘amu’. We also use ‘u’ in place of amu which is known as unified mass.
-In order to take standard elements, scientists took carbon-12 because no other nuclides than carbon-12 have exactly this kind of whole number masses in this scale. We know now that
1 amu = $1.6605 \times {10^{ - 24}}g$ . This unit is used everywhere, from material science to nuclear science, for ions, atoms or any other basic particle.
-To measure masses and relative concentrations of atoms and molecules, mass spectroscopy and mass spectrograph are used. Their principle depends on Newton’s second law of motion and momentum. Thus, determination of atomic masses has become easy nowadays due to the invention of mass spectrometry.

Hence, the correct option is (B).

Note:
One amu can also be called as one Dalton and always remember that we cannot use it for huge and bulky particles. One can make mistakes by thinking that atomic mass is equal to molar mass. But eventually both are different and it is basically the mass of 1 mole of the atoms of the molecule and can be represented in terms of Avogadro’s number i.e. $6.022 \times {10^{23}}$ .