Question

What can be deduced from the symbol $_{\text{2}}{{\text{H}}^{\text{4}}}$ ?
A) An atom of helium contains two electrons
B) An atom of helium contains two protons and four neutrons.
C) The proton (atomic number) of helium is 4
D) Helium acts a diatomic molecule

Answer 1

Helium is a chemical element with the atomic number 2 and the symbol He. It is a colourless, odourless, tasteless, non-toxic, inert monatomic gas that belongs to the noble gas group of the periodic table. It has the lowest boiling and melting points of all the elements. In the visible universe, helium is the second lightest and most plentiful element (hydrogen is the lightest and most abundant).

Complete answer:
The number of protons in the nucleus of every atom of a chemical element is known as the atomic number or proton number (symbol Z). A chemical element's atomic number is the only way to identify it. It is the same as the nucleus' charge number. The atomic number is also equivalent to the number of electrons in an uncharged atom.
The mass number, also termed atomic mass number or nucleon number, is the total amount of protons and neutrons (collectively known as nucleons) in an atomic nucleus. It's about the same as the atom's atomic mass expressed in atomic mass units. Because protons and neutrons are both baryons, their mass number A is the same as the nucleus' baryon number B. (and also of the whole atom or ion). For each isotope of a chemical element, the mass number is different. As a result, the number of neutrons (N) in a particular nucleus is equal to the difference between the mass number and the atomic number
$N\text{ }=\text{ }A\text{ }\text{ }Z$
We may deduce from the symbol $_{\text{2}}{{\text{H}}^{\text{4}}}$ that He has an atomic number of 2 and a mass number of 4.
Its atom has two protons.
In the nucleus, there are protons and neutrons, as well as two electrons.
Hence option A is correct.

Note:
The mass number A of an atom is calculated by adding the atomic number Z and the number of neutrons N. Because protons and neutrons have almost the same mass and the mass defect of nucleon binding is usually tiny compared to the nucleon mass, each atom's atomic mass is within 1% of the full number A when stated in unified atomic mass units.