Question

1. if an isotope of uranium has 92 protons (z = 92) and 143 neutrons, what is the mass number of this isotope? 3) how many neutrons are in the following isotopes? a. $_{19}^{39}k$

Explanation:

Step1: Recall mass - number formula

The mass number (A) of an isotope is the sum of the number of protons (Z) and the number of neutrons (N), i.e., $A = Z+N$.

Step2: Calculate mass number for uranium isotope

Given $Z = 92$ and $N = 143$ for the uranium isotope. Then $A=92 + 143=235$.

Step3: Recall atomic - number concept for potassium

For the potassium isotope $\ce{^{39}_{19}K}$, the atomic number $Z = 19$ and the mass number $A = 39$. Using the formula $N=A - Z$.

Step4: Calculate number of neutrons for potassium isotope

Substitute $A = 39$ and $Z = 19$ into the formula $N=A - Z$. So $N=39 - 19 = 20$.

Answer:

1. 235
2. a. 20