What value of Z (atomic number) and A (mass number) result in the following alpha decay?
A) Z = 92; A = 238
B) Z = 91; A = 238
C) Z = 90; A = 234
D) Z = 93; A = 238
E) Z = 88; A = 236

Question

What value of Z (atomic number) and A (mass number) result in the following alpha decay? 
A) Z = 92; A = 238 
B) Z = 91; A = 238 
C) Z = 90; A = 234 
D) Z = 93; A = 238 
E) Z = 88; A = 236

Quizplus · Accepted Answer

In alpha decay, a nucleus emits an alpha particle, which is composed of 2 protons and 2 neutrons (i.e. a helium nucleus). 
The given alpha decay can be written as: 
             11eb6adc_ed7f_b1c5_b0cf_1d84624c23fc_TB8245_11 --> Z-2, A-4 + 2He4
Here, Z and A are the atomic number and mass number of the parent nucleus, respectively. 
Comparing the given alpha decay with the general form, we can determine the values of Z and A for the parent nucleus: 
             (Z, A) --> (Z-2, A-4)
Therefore, the parent nucleus has Z = 90 (i.e. 92-2) and A = 234 (i.e. 238-4). 
Among the answer choices, only option C has Z = 90 and A = 234.

What Value of Z (Atomic Number) and a (Mass Number)