Question

The mass of one helium atom is:
A. $2amu$
B. $3amu$
C. $4amu$
D. $8amu$

Answer 1

Hint:As we know that atoms are the basic units of matter. There are sub-particles for an atom. They are protons, electrons and electrons. The mass of an atom is known as the atomic mass. It is obtained by adding the number of protons and electrons.

Complete answer:
The positively charged particles are called protons. The negatively charged particles are known as the electrons. While neutrons have neutral charge. Moreover, the electrons are revolving around the nucleus. The protons and neutrons are constituted in the nucleus. The atomic number defines the number of protons or electrons while mass number defines the number of protons and neutrons. But the atomic mass can be obtained by adding the number of protons and neutrons and multiplying by $1amu$.
Atomic mass is expressed in $amu$ units. There are two protons and two neutrons. Thus atomic mass is equal to $4amu$.

Hence,the correct option is C.

Additional information:
Generally helium molecules are produced during a nuclear fission reaction. When a heavy parent nucleus is disintegrated to form lighter daughter nuclei. In some nuclear fission reactions, helium molecules are formed.

Note:
In an atom, the neutron number is always less than the atomic number, i.e. the number of protons. At standard temperature and pressure, when the atomic mass is expressed in gram units, it is known as the mole of a substance. Also, Avogadro number is the number of atoms or molecules or particles in a mole of a substance. Atomic mass of helium can also be expressed in grams. Atomic mass of helium is $4.00g$.