Radioactive element of group 17 is

Options

A. Polonium.
B. Francium
C. Astatine
D. Radium

Answer

To solve the question "Radioactive element of group 17 is," we will follow these steps:

### Step 1: Identify Group 17 Elements
Group 17 of the periodic table is known as the halogen group. The elements in this group include:
- Fluorine (F)
- Chlorine (Cl)
- Bromine (Br)
- Iodine (I)
- Astatine (At)

### Step 2: Determine Radioactive Elements
Among the elements listed in Group 17, we need to identify which one is radioactive. Radioactive elements are those that have unstable nuclei and emit radiation as they decay into other elements.

### Step 3: Analyze Each Element
- **Fluorine (F)**: Stable and non-radioactive.
- **Chlorine (Cl)**: Stable and non-radioactive.
- **Bromine (Br)**: Stable and non-radioactive.
- **Iodine (I)**: While Iodine-131 is radioactive, it is not the only radioactive element in Group 17.
- **Astatine (At)**: Astatine is known to be radioactive. It has no stable isotopes and is the rarest naturally occurring element on Earth.

### Step 4: Confirm the Radioactive Element
Among the elements of Group 17, Astatine (At) is the only element that is classified as radioactive. It has an atomic number of 85 and a half-life of approximately 8.1 hours for its most stable isotope.

### Conclusion
The radioactive element of Group 17 is **Astatine (At)**.

### Final Answer
The correct answer is **C: Astatine**.

---