Constantan is an alloy formed mainly from which combination of metals?

Introduction / Context:
This question tests knowledge of common engineering alloys. Constantan is a special alloy known for having nearly constant electrical resistance over a range of temperatures. Such alloys are widely used in resistance wires and thermocouples. Knowing its composition helps students connect material properties with alloying elements in basic materials science and chemistry.

Given Data / Assumptions:

• The alloy in question is constantan.
• Options list different combinations of metals such as copper, nickel, manganese, chromium, iron, and titanium.
• We assume standard textbook composition where constantan is mainly copper and nickel.

Concept / Approach:
Alloys are mixtures of metals designed to obtain certain properties. Constantan is particularly valued because its resistivity is almost unchanged with temperature. The classic constantan alloy contains about 55 percent copper and 45 percent nickel by mass. While small impurities may exist, these two metals are the primary components. Therefore, among the given options, the pair containing only copper and nickel must be identified.

Step-by-Step Solution:
Step 1: Recall the definition of constantan. Constantan is a copper nickel alloy with almost constant resistivity. Step 2: Scan the options for a copper nickel pair. Option B includes Cu, Ni, and Mn. Option D includes Cu and Ni only. Step 3: Determine which matches the standard composition. Standard constantan is primarily copper and nickel, not a four metal or three metal mixture. Therefore, the correct combination is Cu and Ni.

Verification / Alternative Check:
Reference tables for resistance alloys list constantan as a copper nickel alloy often described by formulas like Cu55Ni45. Some grades may include minor elements but the core remains that constantan is basically a copper nickel system. There is no conventional constantan alloy described by compositions such as Ni Cr Mn Fe, which are more typical of stainless steels or nichrome type alloys, confirming that Cu, Ni is the correct combination.

Why Other Options Are Wrong:
Option A: The combination Ni, Ti, Fe, Cr resembles high strength or stainless alloys rather than constantan and is not the textbook composition. Option B: Cu, Ni, Mn adds manganese, which is part of some other special alloys but is not characteristic of constantan in basic chemistry courses. Option C: Ni, Cr, Mn, Fe suggests stainless steel or heat resistant alloys, not constantan.

Common Pitfalls:
Students sometimes confuse constantan with nichrome or stainless steel, all of which are used as heating elements or resistance materials. Remember that nichrome is based on nickel and chromium, stainless steels are iron based with chromium and sometimes nickel, whereas constantan is specifically a copper nickel alloy. Associating each name with its key metals is a good memory aid.

Final Answer:
Constantan is mainly an alloy of Cu, Ni, that is copper and nickel.