Q1. [4] § Chapter Introduction § 3.1 PHYSICAL PROPERTIES § 3.2 CHEMICAL PROPERTIES OF METALS
Many pure metals like copper, iron and gold are very soft and as such are considered unsuitable for certain uses. Metallic objects around us such as cooking utensils, statues, ornaments, guns etc. are actually not made up of pure metals. Instead of pure metals, alloys are used in the design of most of the useful objects. Making alloys enhances the basic properties of a metal which is the primary constituent (metal) of an alloy.
Read the source and answer the sub-parts that follow.
- (I) How does electrical conductivity and melting point of a metal change when it is converted to its alloy by mixing a small amount of an element in it ? [1]
- (II) Name an alloy used for welding two wires together in an electric circuit. Write its major constituents. [1]
- (III) Answer either (a) or (b). [2]
Previously asked in CBSE board exam
2025 31/6/1 Q37
Generated by claude-sonnet-4-6 · 2026-06-15 06:49 · grounding stimulus
Model Answer
(I) When a metal is converted to an alloy, its electrical conductivity decreases and its melting point also decreases compared to the pure metal.
(II) Solder is used for welding two wires together in an electric circuit.
Major constituents: Lead (Pb) and Tin (Sn) (roughly 1:2 ratio).
(III) (Note: Sub-parts (a) and (b) are not printed in the question. A student should answer whichever option is given in their exam paper. No option text is available here to answer.)
Source: Metals and Non-metals, Alloys section
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Explanation
- For (I), remember the two key changes in properties on alloy formation: electrical conductivity decreases (irregular atomic arrangement resists electron flow) and melting point decreases (e.g., solder melts easily — this is why it's useful for welding wires).
- For (II), solder is the classic CBSE example for electrical welding; always mention both constituents (Pb + Sn) to secure full marks.
- For (III), since the (a)/(b) options were not included in the question as typed, the student must refer to their actual paper and answer accordingly. Common related topics include: amalgams (Hg alloys), steel/stainless steel, or why iron articles are coated with zinc (galvanisation).
If a question refers to an image, map, graph or diagram that is not shown here, find the actual CBSE question paper on the CBSE website:
cbse.gov.in.