Which of the following ions is paramagnetic ?

Question

Accepted Answer

The question asks which of the given ions is paramagnetic. The correct answer is Option 2: $Gd^{3+}$. Let's explore why this is the correct choice and why the other options are incorrect.

1. **Explanation for Option 2: $Gd^{3+}$**
   - Gadolinium (Gd) is an element in the lanthanide series, and its atomic number is 64. The electron configuration of a neutral gadolinium atom is [Xe] 4f^7 5d^1 6s^2. When it loses three electrons to form the $Gd^{3+}$ ion, the electron configuration becomes [Xe] 4f^7.
   - The 4f^7 configuration means that there are seven unpaired electrons in the 4f subshell. According to Hund's rule, these unpaired electrons result in a high degree of paramagnetism. Therefore, $Gd^{3+}$ is paramagnetic due to the presence of these unpaired electrons.

2. **Explanation for why other options are incorrect:**

- **Option 1: $La^{3+}$**
     - Lanthanum (La) has an atomic number of 57, and its electron configuration is [Xe] 5d^1 6s^2. When it forms the $La^{3+}$ ion, it loses three electrons, resulting in the electron configuration [Xe].
     - The [Xe] configuration corresponds to a completely filled shell with no unpaired electrons. As a result, $La^{3+}$ is diamagnetic, not paramagnetic.

- **Option 3: $Lu^{3+}$**
     - Lutetium (Lu) has an atomic number of 71, and its electron configuration is [Xe] 4f^14 5d^1 6s^2. When it forms the $Lu^{3+}$ ion, it loses three electrons, resulting in the electron configuration [Xe] 4f^14.
     - The 4f^14 configuration is fully filled with no unpaired electrons, making $Lu^{3+}$ diamagnetic.

- **Option 4: $Ce^{4+}$**
     - Cerium (Ce) has an atomic number of 58, and its electron configuration is [Xe] 4f^1 5d^1 6s^2. When it forms the $Ce^{4+}$ ion, it loses four electrons, resulting in the electron configuration [Xe].
     - Similar to $La^{3+}$, the [Xe] configuration is fully filled with no unpaired electrons, making $Ce^{4+}$ diamagnetic.

In summary, $Gd^{3+}$ is the only ion among the options that has unpaired electrons in its electron configuration, specifically in the 4f subshell, which makes it paramagnetic. The other ions have either completely filled electron configurations or no unpaired electrons, resulting in diamagnetic properties. Therefore, Option 2 is correctly identified as the paramagnetic ion.