Which of the following `"is"//"are"` true?

Options

A. The most radioactive element present in pitchblende is uranium.
B. `P-32` is used for the treatment of leukaemia.
C. `CO_(2)` present in the air contains `C-12` only.
D. Omission of `gamma`-rays changes the mass number but not atomic number.

Answer

To determine which of the given statements are true, let's analyze each statement one by one.

### Step 1: Analyze Statement A
**Statement A:** The most radioactive element present in pitchblende is uranium.

- **Explanation:** Pitchblende is a mineral ore that primarily contains uranium oxides. Uranium is indeed the most significant and radioactive element found in pitchblende. Therefore, this statement is **true**.

### Step 2: Analyze Statement B
**Statement B:** P-32, an isotope of phosphorus, is used for the treatment of leukemia.

- **Explanation:** P-32 (Phosphorus-32) is a radioactive isotope of phosphorus that is used in medical treatments, including for certain types of leukemia. Thus, this statement is also **true**.

### Step 3: Analyze Statement C
**Statement C:** The carbon dioxide present in the air contains mainly C-12 isotope.

- **Explanation:** Carbon dioxide (CO2) in the atmosphere is primarily composed of carbon isotopes. Approximately 99% of carbon in CO2 is C-12, while the remaining 1% consists of C-13 and C-14 isotopes. The statement claims that it contains mainly C-12, which is correct in terms of proportion, but it does not specify that there are other isotopes present. However, the statement is misleading as it implies that only C-12 is present. Therefore, this statement is **incorrect**.

### Step 4: Analyze Statement D
**Statement D:** The emission of gamma rays changes the mass number but not the atomic number.

- **Explanation:** When a radioactive element emits gamma rays, there is no change in either the mass number or the atomic number. Gamma emission involves the release of energy without altering the composition of the nucleus. Therefore, this statement is **incorrect**.

### Conclusion
Based on the analysis:
- Statement A is **true**.
- Statement B is **true**.
- Statement C is **incorrect**.
- Statement D is **incorrect**.

Thus, the true statements are **Statement A and Statement B**.

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