There are four radioactive decay series called thorium `(4n)`, uranium `(4n + 2)` actinium `(4n + 3)` and neptunium `(4n + 1)` series. Neptunium series is artificial while other three series are natural. The end productsd of each radioacitve decay series have stable nuclei. All natural decay series terminate at lead but neptunium or artificial series terminate at bismuth.
`._(86)Rn^(219)` is a member of actinium series. Another member of same series is

Options

A. `._(92)U^(235)`
B. `._(89)Ac^(222)`
C. `._(90)Th^(212)`
D. `._(84)Po^(212)`

Answer

To solve the problem, we need to identify another member of the actinium decay series, given that radon-219 (Rn-219) is a member of this series. The actinium series is characterized by the formula \(4n + 3\), where \(n\) is a non-negative integer. This means that when the mass number of an element in this series is divided by 4, the remainder should be 3.

### Step-by-Step Solution:

1. **Identify the Mass Number of Rn-219**:
- The mass number of radon is 219.

2. **Check the Remainder of Rn-219**:
- Divide 219 by 4:
\[ 219 \div 4 = 54 \quad \text{(with a remainder of 3)} \]
- Since the remainder is 3, Rn-219 indeed belongs to the actinium series.

3. **Identify Other Members of the Actinium Series**:
- We need to find another element whose mass number, when divided by 4, also gives a remainder of 3.

4. **Check the Mass Number of Uranium-235**:
- The mass number of uranium is 235.
- Divide 235 by 4:
\[ 235 \div 4 = 58 \quad \text{(with a remainder of 3)} \]
- Since the remainder is also 3, uranium-235 (U-235) is another member of the actinium series.

5. **Check Other Options**:
- We can check other elements like actinium-227 (Ac-227) and polonium-212 (Po-212) to confirm they do not belong to the actinium series:
- For Ac-227:
\[ 227 \div 4 = 56 \quad \text{(with a remainder of 3)} \]
- Ac-227 also belongs to the actinium series.
- For Po-212:
\[ 212 \div 4 = 53 \quad \text{(with a remainder of 0)} \]
- Po-212 does not belong to the actinium series.

6. **Conclusion**:
- Therefore, both uranium-235 and actinium-227 are members of the actinium series along with radon-219.

### Final Answer:
Another member of the actinium series is **Uranium-235 (U-235)**.