Which of the following is NOT ferromagnetic in nature ?

Options

A. Ni
B. Co
C. `CrO_(2)`
D. O_(2)

Answer

To determine which of the following substances is NOT ferromagnetic in nature, let's analyze each option provided:

1. **Nickel (Ni)**: Nickel is a well-known ferromagnetic material. It has a high magnetic permeability and retains its magnetization even after the external magnetic field is removed.

2. **Cobalt (Co)**: Cobalt is also a ferromagnetic material. Similar to nickel, it exhibits strong magnetic properties and can be magnetized.

3. **Chromium Dioxide (CrO2)**: Chromium dioxide is known to exhibit ferromagnetic properties as well. It is used in magnetic recording media and has a significant magnetic moment.

4. **Oxygen (O2)**: Oxygen, in its molecular form (O2), is not ferromagnetic. Instead, it is classified as paramagnetic, meaning it is attracted to magnetic fields but does not retain magnetization once the external field is removed.

Based on this analysis, the substance that is NOT ferromagnetic in nature is:

**Answer: Option 4 - O2**