Assertion: A transistor can be used as an amplifier.
Reason: A small change in input current can change output on a large scale.

Answer

To solve the question regarding the assertion and reason about transistors, we can break it down into clear steps:

### Step 1: Understand the Assertion
The assertion states that "A transistor can be used as an amplifier."
- **Explanation**: This is true. Transistors are widely used in electronic circuits as amplifiers. They can take a small input signal and produce a larger output signal, which is the fundamental operation of an amplifier.

### Step 2: Understand the Reason
The reason states that "A small change in input current can change output on a large scale."
- **Explanation**: This statement is also true. In a transistor, a small change in the input current (or voltage) can lead to a significant change in the output current. This property is what allows transistors to amplify signals.

### Step 3: Analyze the Relationship
Now we need to determine if the reason correctly explains the assertion.
- **Explanation**: The reason provided explains how transistors amplify signals. The ability of a transistor to produce a large output from a small input is indeed the principle behind its use as an amplifier. Therefore, the reason supports the assertion.

### Step 4: Conclusion
Based on the analysis:
- Both the assertion and the reason are correct, and the reason is a correct explanation of the assertion.

### Final Answer
- **Assertion**: True
- **Reason**: True
- **Conclusion**: Both assertion and reason are correct, and the reason is a correct explanation of the assertion.

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