Question

Which of the following may contain two neutrons and two protons?
A. $He$
B. ${D_2}$
C. $He_2^{2 + }$
D. ${H_2}$

Answer 1

In order to answer this question, we should have an idea of the periodic table. We know that electrons, protons and neutrons are three subatomic particles of an atom. Protons are the positively charged species whereas electrons are the negatively charged species. The neutral are neutral in nature.

Complete answer:
Let us completely understand the answer to this question in complete detail.
As we all know, the number of electrons and the number of protons are equal to the atomic number of the element. In other words, we can say that the atomic number of an element is the number of electrons present in the element. Also, we know that the number of electrons is equal to the number of protons due to which atom is electrically neutral.
Now, in this question, just identify the number of protons, electrons and neutrons for each option.
In option A- the atomic number of helium is $2$ which indicates the number of electrons is $2$ which is also equal to the number of protons i.e. $2$ . Also, here the number of neutrons is also $2$ .
In option B- Deuterium is given which is an isotope of hydrogen atom. The number of electrons is $1$ in a single deuterium atom. Here, two deuterium atoms are given, so the number of electrons as well as protons is $2$ . Also, here the number of neutrons is also $2$ .
In case of option C, two helium molecules are given i.e. $4$ electrons as well as protons, but here $+ 2$ is given which indicates two electrons are lost. Then, the number of electrons becomes $2$ but the number of protons remains $4$ only.
In option D, one hydrogen molecule ( ${H_2}$ ) is given which indicates $2$ electrons as well protons. But there are no neutrons.
Hence, the correct answer is option (A) and (B).

Note:
It must be remembered that the number of electrons or protons are equal to the atomic number of the element. Also, the three subatomic particles of an atom. First, protons which are the positively charged species whereas electrons are the negatively charged species. The neutral are neutral in nature.