Question

Particles which can be added to the nucleus of an atom without changing its chemical properties are called

• A. neutrons
• B. electrons
• C. protons
• D. alpha particles

Answer 1

The correct option is A

neutrons

Explanation for correct option:

(a) Neutrons:

1. Consider an element with a chemical symbol${}_{\text{z}}{\text{X}}^{\text{A}}$.
2. Here, $Z$ is the atomic number, i.e., the number of protons or electrons in the atom and $A$ is the mass number, i.e., the sum of a number of protons and neutrons in the nucleus.
3. Adding a neutron (${}_0{n}^1$) results in the following -

${}_{\text{Z}}{\text{X}}^{\text{A}}{+}_0{n}^1\to {}_{\text{Z}}{\text{X}}^{\text{A+1}}$

4. Thus, the number of a proton (and electrons) remains unchanged.

Explanation for incorrect options:

(b) Electrons:

1. Adding an electron (${}_{-1}{e}^0$) to the element makes the following change –

${}_{\text{Z}}{\text{X}}^{\text{A}}{+}_{-1}{e}^0\to {}_{\text{Z-1}}{{\text{Y}}_1}^{\text{A}}$

2. Thus, the number of protons is changed. And a new element is formed.

(c) Protons:

1. Adding a proton (${}_1{p}^1$) to the element makes the following change –

${}_{\text{Z}}{\text{X}}^{\text{A}}{+}_1{p}^1\to {}_{\text{Z+1}}{{\text{Y}}_2}^{\text{A+1}}$

(d) Alpha particle:

1. The symbol of an alpha particle is, ${}_2{\alpha }^4$
2. Adding an alpha particle to the element makes the following change –

${}_{\text{Z}}{\text{X}}^{\text{A}}{+}_2{\alpha }^4\to {}_{\text{Z+2}}{{\text{Y}}_3}^{\text{A+4}}$

Hence, the correct option is (a).