The constituent common to duralumin and alnico is

1. Analyze the question We need the element present in both alloys: duralumin and alnico.

2. Explain the concept An alloy is a mixture of a metal with other elements, made to improve properties like strength, hardness, or magnetism.

3. Composition of each alloy

• Duralumin: Aluminium (about 95%), copper (about 4%), magnesium (about 0.5%), manganese (about 0.5%). It is light and strong, used in aircraft parts.
• Alnico: The name comes from Aluminium, Nickel, and Cobalt, with iron and sometimes copper. It is used to make strong permanent magnets.

4. Compare the options

• A. Co (cobalt): in alnico only, not in duralumin.
• B. Mn (manganese): in duralumin only.
• C. Al (aluminium): in both.
• D. Mg (magnesium): in duralumin only.

5. Answer The common constituent is Aluminium (Al), which is option C.

Exam tip: Look at the name "Al-Ni-Co": it spells out its own ingredients. And "duralumin" has "alum" in it, which points to aluminium. Whenever you see these two alloys together, think aluminium.