A wire-bound standard resistor uses manganin or constantan. It is because

Standard resistors require high stability to ensure that their resistance value does not fluctuate with environmental changes. Alloys like manganin (copper, manganese, and nickel) and constantan (copper and nickel) are specifically chosen for wire-bound standard resistors because they possess an extremely low temperature coefficient of resistance [1]. This property means their resistivity remains almost unchanged over a wide range of temperatures. While pure metals exhibit a significant increase in resistivity as temperature rises due to increased atomic vibrations and electron collisions, these specific alloys are engineered to have a 'close to zero' temperature dependence. This stability is critical for precision measurements where a temperature-independent resistance standard is required. Although alloys generally have higher resistivity than their constituent pure metals, the primary reason for their use in standard resistors is this thermal stability rather than the magnitude of resistivity itself.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > Activity 11.3 > p. 178