Chapter 40, Problem 25A

(a)

To determine

The ranking of the nuclei by the number of protons in the nucleus.

Explanation of Solution

Introduction:

The number of protons in the nucleus remains same and only number of neutrons changes in the nucleus.

The number of protons in the nucleus of ${}_{92}^{238}\text{U}$ is 92. The number of protons in the nucleus of ${}_{90}^{239}\text{Th}$ is 90. The number of protons in the nucleus of ${}_{94}^{239}\text{Pu}$ is 94. The number of protons in the nucleus of ${}_{93}^{239}\text{Np}$ is 93.

Conclusion:

Thus, the ranking of nuclei according to number of proton in nucleus is C, D, A, B.

(b)

To determine

The ranking of the nuclei by the number of neutrons in the nucleus.

Explanation of Solution

Introduction:

The number of neutrons in the nucleus of atom.is equal to the difference of mass number and atomic number.

The atomic number and mass number of ${}_{92}^{238}\text{U}$ is 92 and 238. So, the number of neutrons in the nucleus is 146.

The atomic number and mass number of ${}_{90}^{239}\text{Th}$ is 90 and 239. So, the number of neutrons in the nucleus is 149.

The atomic number and mass number of ${}_{94}^{239}\text{Pu}$ is 94 and 239. So, the number of neutrons in the nucleus is 145.

The atomic number and mass number of ${}_{93}^{239}\text{Np}$ is 93 and 239. So, the number of neutrons in the nucleus is 146.

Conclusion:

Thus, the ranking of nuclei according to number of neutrons in nucleus is B, A = D, C.