The decay of a radioactive element follows first order kinetic. Thus,

Options

A. Half-life period `= a` constant`//K`,
B. The rate of decay is independent of temperature
C. The rate can be altered by changing chemical conditions
D. The element will be completely transformed into new element after expiry of two half-life period

Explanation

To solve the question regarding the decay of a radioactive element that follows first-order kinetics, we will analyze each statement provided in the options.

### Step-by-Step Solution:

1. **Understanding First-Order Kinetics**:
- In first-order kinetics, the rate of decay of a radioactive substance is proportional to the amount of substance remaining. The mathematical expression for the half-life (t_half) is given by:
\[ t_{1/2} = \frac{0.693}{k} \]
- Here, \( k \) is the decay constant.

2. **Analyzing the Statements**:
- **Statement A**: "Half-life period (t_half) is equal to a constant upon k."
- This statement is true because it directly corresponds to the formula for half-life in first-order kinetics.

- **Statement B**: "The rate of decay is independent of temperature."
- This statement is false. The decay constant \( k \) is temperature-dependent; as temperature changes, the rate of decay changes as well.

- **Statement C**: "Rate of decay can be altered by changing the chemical conditions."
- This statement is also false. The decay of a radioactive element is a spontaneous process and is not affected by chemical conditions such as pressure or temperature.

- **Statement D**: "This element will be completely transformed into a new element after the expiry of two half periods."
- This statement is incorrect. After one half-life, the quantity of the radioactive element is halved, and after two half-lives, it is reduced to a quarter of the original amount. It will not be completely transformed into a new element after two half-lives.

3. **Conclusion**:
- The only true statement among the options is Statement A. Therefore, the correct answer is:
\[ \text{Correct Answer: Option A} \]