Question

The number of atoms of the $He$ in $104$ $amu$is:
A. $3.1 \times {10^{25}}$
B. $6.2 \times {10^{25}}$
C. $26$
D. $206$

Answer 1

Hint: Here in the question the abbreviation used $amu$ stands for the atomic mass unit. Every element is having some of its unique atomic mass unit. The atomic mass unit of the helium $He$ atom is four (4) atomic mass units.

Complete answer:
So, the atomic mass unit of the helium atom= $4$ $amu$
This implies that the $4$ $amu$ of helium = 1 atom of the helium atom
So, the number of the atoms in the $104$ $amu$= $\dfrac{{104}}{4} = 26$
Hence, The number of atoms of the $He$ in $104$ $amu$ is $26$.

So, the correct answer is “Option C”.

Additional Information:
The definition of the one atomic mass unit can be written as follows:
An atomic mass unit which is represented as a symbol in AMU or amu form. It is defined as precisely $\dfrac{1}{{12}}th$ the mass of an atom of Carbon-12. The Carbon-12 atom has six protons and six neutrons in its nucleus. In other words, one AMU is the average of the proton rest mass and the neutron rest mass. That means the mass of an atom in AMU is roughly equal to the sum of the number of protons and neutrons in the nucleus. The AMU is used to express the relative masses of, and thereby differentiate between, various isotopes of elements. Sometimes there is a confusion between the concept of the molar mass and the atomic mass unit. Molar mass is the mass of one mole of a substance. Atomic mass is the mass of one individual unit of a substance. the atomic mass in amu of a substance is numerically equivalent to the mass in g of one mole of that substance.

Note:
The mass of one mole of atoms of a pure element in grams is equivalent to the atomic mass of that element in atomic mass units (amu) or in grams per mole (g/mol). Although mass can be expressed as both amu and g/mol, g/mol is the most useful system of units for laboratory chemistry.