Radioactive disintegration is a `……………….` order reaction.

Answer

To solve the question regarding the order of radioactive disintegration, we can follow these steps:

### Step 1: Understand Radioactive Disintegration
Radioactive disintegration refers to the process by which unstable atomic nuclei lose energy by emitting radiation. This process results in the transformation of the radioactive material into a different element or isotope.

**Hint:** Think about what happens to radioactive materials over time and how they change.

### Step 2: Identify the Rate of Disintegration
The rate of disintegration of a radioactive substance is defined as the number of undecayed nuclei that disappear per unit time. This can be expressed mathematically.

**Hint:** Consider how the rate of a reaction is related to the concentration of the reactants.

### Step 3: Establish the Relationship
The rate of disintegration is directly proportional to the number of undecayed atoms present. This can be expressed as:
\[ \text{Rate} \propto [N] \]
where \([N]\) is the concentration of undecayed nuclei.

**Hint:** Recall that in chemical kinetics, the rate of a reaction can be expressed in terms of the concentration of reactants.

### Step 4: Determine the Order of Reaction
In the context of reaction order, if the rate is directly proportional to the concentration of the reactants raised to the power of one, then it is classified as a first-order reaction. Thus, we can write:
\[ \text{Rate} = k[N]^1 \]
where \(k\) is the rate constant.

**Hint:** Remember that the exponent in the rate equation indicates the order of the reaction.

### Step 5: Conclusion
Since the rate of disintegration of radioactive nuclei is directly proportional to the concentration of undecayed atoms, we conclude that radioactive disintegration is a first-order reaction.

**Final Answer:** Radioactive disintegration is a **first-order reaction**.

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