Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Alloys such as constantan and manganin are used in making standard resistance coils.
Reason R: Constantan and manganin have very small value of temperature coefficient of resistance.
In the light of the above statements, choose the correct answer from the options given below.

We have the Assertion that alloys such as constantan and manganin are used in making standard resistance coils, and the Reason that these alloys have a very small value of temperature coefficient of resistance.

The assertion is true because constantan and manganin are indeed the preferred materials for standard resistance coils used in precision instruments like Wheatstone bridges and potentiometers.

The reason is also true: these alloys have extremely low temperature coefficients of resistance (of the order of $$10^{-5}$$ per °C), which means their resistance remains nearly constant over a wide range of temperatures.

Now, the reason correctly explains the assertion, because the primary requirement for a standard resistance coil is that its resistance should not change appreciably with temperature. Since constantan and manganin satisfy this requirement owing to their very small temperature coefficient of resistance, R is indeed the correct explanation for A.

Hence, the correct answer is Option 1.