Assertion :Vacuum tube is used in electron microscope. Reason: The electrons move only in a straight line in vaccum.

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

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Assertion is correct but Reason is incorrect.

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Assertion is incorrect but Reason is correct.

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Solution

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
In vacuum tubes, hot cathode or thermionic cathode is used. It is a cathode electrode that is heated to make it emit electrons due to thermionic emission. Hot cathodes are used as the source of electrons in equipments such as electron microscope. So, Assertion is correct and so is Reason with Reason being the explanation of Assertion.

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