Actinides

Options

A. are all synthetic elements
B. include elements 104
C. have any short lived isotopes
D. have variable valency

Explanation

### Step-by-Step Solution:

1. **Understanding Actinides**:
- Actinides are a series of 15 elements in the periodic table that range from atomic number 89 (actinium) to 103 (lawrencium).
- They include both naturally occurring elements and synthetic elements.

2. **Identifying Natural and Synthetic Elements**:
- The actinides include natural elements such as actinium, thorium, and uranium.
- Elements with atomic numbers greater than 92 (uranium) are primarily synthetic.

3. **Isotopes of Actinides**:
- Isotopes are variants of elements that have the same number of protons but different numbers of neutrons.
- Uranium and thorium have both long-lived and short-lived isotopes, which means they can exist in stable forms for extended periods.

4. **Valency of Actinides**:
- Actinides exhibit variable valency, meaning they can form compounds in multiple oxidation states. This is a characteristic feature of these elements.

5. **Evaluating Options**:
- Check the given options against the facts established:
- "All are synthetic elements" - Incorrect, as some are natural.
- "Include element 104" - Incorrect, as actinides only go up to element 103.
- "Only short-lived isotopes" - Incorrect, as uranium and thorium have long-lived isotopes.
- "Variable valency" - Correct, as actinides do exhibit variable valency.

6. **Conclusion**:
- The only correct statement about actinides is that they have variable valency.