Question

A certain nucleus A (mass number 238 and atomic number 92) is radioactive and becomes a nucleus (mass number 234 and atomic number 90) by the loss of a particle. (b) Explain how you arrived at your answer.

• A. $90$
• B. $30$
• C. $60$
• D. $80$

Answer 1

The correct option is A $90$

The nucleus undergone a radio active decay (here alpha decay)

By emitting an alpha particle transformed in to a new nucleus

i.e., from ${}^{238}{U}_{92}$ to ${}^{234}T{h}_{90}$

The dsintegration can be explained by the eqn:

${}^A{X}_Z$ ------ ${}^{A-4}{Y}_{Z-2}{+}^{4}H{e}_2$

where, ${}^A{X}_Z$ --- Parent Nucleus

${}^{A-4}{Y}_{Z-2}$ ---- Daughter nucleus

${}^{4}H{e}_2$ ---- Alpha Particle (He Nucleus)

As a result the mass of of the parent nucleus i.e., $238$ reduced by $4$ and became $234$ and the atomic no. $92$ reduced by $2$ and became $90$.

Here decay takes place spontaneously ( without the help of an externanal energy source)

The enrgy difference between the reactants and products will appear as kinetic energy of the produced particles.