Question

Among the following quantities:
i) mass number
ii) average mass of a Carbon atom in amu
iii) the charge of nucleus in amu and
iv) mass of a Carbon-12 atom in grams

A) only (i) is a whole number
B) only i) and (iii) are whole number
C) only i) and (iv) are whole numbers
D) only iii) and (iv) are whole numbers

Answer 1

Hint: We have to consider all these options properly. After analysis we are able to find which one is the whole number.The mass number, also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus.The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance (the decimal associated with percent of atoms of that element that are of a given isotope).

Complete step by step answer:
1) The mass number is always the whole number because the mass number is the total number of
neutrons and protons in the nucleus of the atom and an atom never contains fractional or an
integer number of protons or neutrons.
2) Average mass of the carbon atom in amu is $12.011 \mathrm{u}$. It is in decimal and can be written as
fractional form.
3) Charge on the nucleus in amu:- Charge on the nucleus is equal to the number of protons and
The number of protons is always whole.
4) Mass of carbon atom = (Mass of carbon/Avogadro number)
$=\left(12 \mathrm{g} / 6.022 \mathrm{X} 10^{23}\right)=1.99 \mathrm{X} 10^{-23}$ grams. Never a whole number.
So, the correct answer is “Option B”.

Note: Avogadro number is equal to $6.022 \times 10^{23}$. Average mass of the carbon atom in amu is $12.011 \mathrm{u}$.